In the Air (Life on Earth) 9780816050499, 081605049X

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LIFE ON EARTH

IN THE AIR

THE DIAGRAM GROUP

Life On Earth: In the Air Copyright © 2004 by The Diagram Group Written, edited, and produced by Diagram Visual Information Ltd Editorial director:

Denis Kennedy

Editors:

Bender Richardson White, Gordon Lee

Contributor:

John Stidworthy

Indexer:

Martin Hargreaves

Art director:

Roger Kohn

Senior designer:

Lee Lawrence

Designers:

Anthony Atherton, Christian Owens

Illustrators:

Pavel Kostal, Kathleen McDougall, Sean Milne, Coral Mula, Graham Rosewarne

Picture researcher:

Neil McKenna

All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Facts On File, Inc. 132 West 31st Street New York NY 10001 For Library of Congress Cataloging-in-Publication Data, please contact Facts On File, Inc. ISBN 0-8160-5049-X Facts On File books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions. Please call our Special Sales Department in New York at 212/967-8800 or 800/322-8755. You can find Facts On File on the World Wide Web at: http://www.factsonfile.com Printed in the United States of America EB Diagram

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This book is printed on acid-free paper.

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Contents 4 Introduction RIDERS AND GLIDERS 6 The atmosphere 8 Aerial plankton 10 Gliding reptiles and amphibians 12 Gliding reptiles of the past 14 Flying squirrels 16 Pouched gliders and colugos FIRST FLYERS 18 First flying insects 20 Insect wings 22 Hot flyers 24 Big wings 26 Two wings 28 Hidden wings VERTEBRATES CONQUER THE AIR 30 Evolution of pterosaurs 32 Pterosaur wings 34 Tailed pterosaurs 36 Pterodactyls 38 Pterosaur lifestyles 40 The greatest flyer ever BIRDS TAKE OVER 42 Evolution of birds 44 Archaeopteryx 46 Other early birds 48 Feathers 50 The bird wing 52 Flight 54 Fast flyers 56 Hanging in the air

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Patrolling the oceans Hoverers Aerial courtship Finding fruit Catching insects Trawling the aerial plankton 70 Silent flight 72 Birds of a feather FLYING MAMMALS 74 Evolution of bats 76 Bat wings 78 How well do they fly? 80 Finding the way 82 Bats and gnats 84 Carnivorous bats 86 Vampires 88 Fruit bats 90 Flower bats MIGRATION 92 Why migrate? 94 Homing 96 Insect migration 98 Bat migration 100 Bird migration 102 The greatest journeys 104 Timeline 106 Glossary 109 Websites to visit 111 Index

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Main Introduction head

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HIS BOOK is a concise, illustrated guide to living things that evolved to fly and make use of the airspace that encircles our planet. Texts, explanatory diagrams, illustrations, captions, and feature boxes combine to help readers grasp important information. A glossary clarifies the more difficult scientific terms for younger students, while a list of websites provides links to other relevant sources of additional information. Chapter 1, Riders and Gliders, looks at animals that either passively float or glide through the air. Present-day mammals, reptiles, and amphibians are covered, together with ancient reptiles from hundreds of millions of years ago. Chapter 2, First Flyers, features the evolution of powered flight in early insects, and its development in modern types ranging from dragonflies to beetles. Chapter 3, Vertebrates Conquer the Air, describes the evolution and progression of the first backboned animals to truly fly, the pterosaurs. It features a range of types from the earliest to the last species before the group became extinct. Chapter 4, Birds Take Over, looks at how birds evolved from dinosaurs. It describes some of the earliest birds known, and shows the many ways that birds have been able to exploit their flying ability. Chapter 5, Flying Mammals, features bats, one of the largest and most varied mammal groups. It gives a glimpse into the many adaptations of this fascinating, and, to humans, largely hidden group. Chapter 6, Migration, features the variety of seasonal journeys made by flying animals, explaining their purpose, and the amazing distances and feats of navigation involved. In the Air is one of six titles in the Life On Earth series that looks at the evolution and diversity of our planet, its features, and living things, both past and present.

The series features all life-forms, from bacteria and algae to trees and mammals. It also highlights the infinite variety of adaptations and strategies for survival among living things, and describes different habitats, how they evolved, and the communities of creatures that inhabit them. Individual chapters discuss the characteristics of specific taxonomic groups of living things, or types of landscape or planetary features. Life On Earth has been written by natural history experts and is generously illustrated with line drawings, labeled diagrams, and maps. The series provides students with a solid, necessary foundation for their future studies in science.

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The atmosphere

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BOUT HALF THE SOLAR RADIATION that reaches the Earth touches the surface, maintaining temperatures that are suitable for life. Other radiation is reflected back from the upper layers of the atmosphere, or heats the thermosphere 200 miles (320 km) above the surface. The stratosphere, from 7 miles (11 km) to 30 miles (48 km) above the Earth, contains the ozone layer, which filters out harmful ultraviolet radiation before it reaches the surface. The troposphere, from ground level to an average of about 7 miles (11 km) up, is the layer where most clouds are formed and where “weather” happens. This layer is twice as thick at the equator as at the poles. In the troposphere, the temperature drops as the altitude increases. At the top of the troposphere, a “jet stream” may be

30 miles (48 km)

Weather balloons

20 miles (32 km) Military aircraft

Ozone layer

The Earth’s atmosphere extends upward from the land’s surface for 440 miles (700 km), and then shades into outer space. However, 75 percent of the mass of the atmosphere is within 7 miles (11 km) of the Earth’s surface. Most of the living things in the air are within a few feet (meters) of the ground.

Supersonic jet

Lower atmosphere Although the Earth’s atmosphere extends a long way above the ground, only the lower layers have sufficient oxygen, a comfortable temperature, and air pressure sufficient to sustain most forms of life.

10 miles (16 km) Mount Everest Jumbo jet

Birds

Clouds

IT’S A FACT Airliners enter the stratosphere, some going as high as 7.5 miles (12 km) with supersonic jets able to fly at an altitude of 11 miles (18 km). Unprotected humans cannot go so high—most would have trouble breathing the thin atmosphere at the top of the world’s highest mountains. Most animals are confined to the lower parts of the troposphere, though some birds can fly up to 5 miles (8 km) high.

Nitrogen

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Composition of the air Carbon dioxide

Argon

Traces Water Oxygen

encountered, a core of high-speed wind up to 300 miles (480 km) wide, traveling at speeds up to 200 miles per hour (320 kmph). The air we breathe at the surface is roughly 21 percent oxygen, 76 percent nitrogen, 1 percent argon, 1 percent water, and 0.03 percent carbon dioxide, with traces of other gases. The composition of the air has probably been much the same for one billion years, including all the time there have been many-celled plants and animals on the Earth. In the early stages of Earth’s history it was probably quite different, with no oxygen, but plenty of carbon dioxide, water, and nitrogen. Once bacteria and single-celled plants started to photosynthesize, building food out of sunlight, water, and carbon dioxide, and producing oxygen in the process, the atmosphere changed to that which we breathe today. In contrast to water, which supports the weight of animals well, air is very thin, and provides little mechanical support. Specialized large surfaces—wings—are needed to lift the weight of a creature and propel it through the air. Only four groups of animals in the world’s history have developed the capacity for flight—insects, birds, bats, and among the extinct reptiles, the pterosaurs. Each group developed a different type of wing.

Composition (above) The same gases have made up most of the Earth’s atmosphere for a long time, although the actual proportions may have varied. In the present day, carbon dioxide levels in the atmosphere are rising, probably due to human activity.

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IN THE AIR RIDERS AND GLIDERS

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Aerial plankton

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RINE SHRIMPS live in temporary pools in Just as plankton is carried in the desert. They lay tiny eggs. Once dried out, the eggs are so light they are spread by the water currents of the sea, the wind to a new home. Small flies and air currents can carry living mosquitos are carried long distances and to great creatures. Bacteria have been heights by air currents. Aphids, too, are slow flyers found in air 26 miles (42 km) that can easily be blown off course, and may float above the Earth. Plant seeds high above the ground. These small insects make may be wafted on a large part of the food of birds that trawl parachutes, or may be so through the air. light that the wind carries “Thunderflies” are sometimes prominent in them. Some animals aerial plankton. These are not flies, but thrips, regularly become part of the insects of the bug group. Although tiny, they have “aerial plankton.” mouthparts adapted for sucking plants. Some are agricultural pests. Their wings are feathery. They gather on top of plants on warm, still days, and launch into flight. Even small air movements buoy them up, transporting them many miles (kilometers). Though tiny, they are numerous, and a meadow on a summer’s day may have several tons (tonnes) of thrips stacked in the column of air above it. Into the air Aphids can be carried high as aerial plankton.

Aphid close-up Some aphids are pests, sucking juices through mouthparts, and sometimes even spreading disease.

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IN THE AIR RIDERS AND GLIDERS

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Young spiders disperse using the wind: they stand in a prominent position and let out a thread or two of silk from their spinnerets. They balance on tiptoe, waiting for the wind to catch their silk parachutes, and then they let go. Large numbers of spiders may fill the air with shimmering strands. They are carried huge distances, not always to places where they can survive. They may be carried to sea. One day, as Darwin traveled round the world, the rigging of his ship was covered with baby spiders, although it was 60 miles (100 km) off the coast of South America. Spiders and insects may be carried high onto mountains. Snows on the summits are sometimes peppered with windborne insects, providing a temporary feast for alpine birds.

Preparing to fly A baby spider lets out a thread of silk before takeoff.

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Victims These tiny insects have little control over where they are carried.

IT’S A FACT Strong winds associated with major storms or tornadoes can lift animals much bigger than insects into the air. “Rains” of frogs, fish, or larger animals are sometimes reported. Even cows have been picked up and later dropped onto treetops.

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Gliding reptiles and amphibians

Among living reptiles and amphibians there are none that truly fly, but a number are able to parachute down from the trees, or even manage a controlled downward glide.

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REE FROGS often have the ends of their toes expanded into “suckers” to help them grip as they climb. A few species of tree frog have enormously expanded webs between the toes of their front and hind feet. If they jump or fall from a tree they keep the body rigid, stretch out their limbs, and spread the web on all four feet. This slows the fall, and allows the frog to land softly in an upright position, ready to move again. One species, the Malaysian flying frog, is famous for its parachuting habits, but it does not really fly, and has very limited control over the direction of its fall. Among the lizards are several species of “flying dragon” in Southeast Asia. In spite of their name, they are only 8 to 16 inches (20 to 40 cm) long, and delicately built. They do have “wings.” These are areas of expandable skin that can be stretched out from the side of the body by enormously elongated ribs. The ribs can

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IT’S A FACT The flying dragon has at times been seen to glide 200 feet (60 m) between trees.

Preparing to fly The flying dragon expands its ribs to sail through the air.

IN THE AIR RIDERS AND GLIDERS

Adapted to fall A light build, and skin fringes, make flying geckos effective parachutists.

Aerial movement To move between trees, the “flying” snake does not need to come to the ground.

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open and shut rather like a fan. While the dragon is running along a branch, its ribs are folded, but it can launch itself from the branch, spreading its wings to glide to another tree. The animal glides down at an angle of about 20 degrees across a clearing before it lands on a tree trunk. It seems well controlled in its descent, and lands with its head pointing up the trunk, ready to climb again. Some other tree lizards can glide with few special adaptations other than being able to flatten the body during descent. The “flying geckos” of Southeast Asia have scaly fringes along the sides of the body and tail, and webs between the toes. Their main function may be camouflage, and there is no muscle to stretch them, but they can still serve as a very effective parachute if the gecko planes to the ground. Perhaps the most unexpected “flying” reptile is the flying snake Chrysopelea. Like the flying dragons and geckos it lives in southern Asia. Normally a skinny cylindrical shape, it is a very good climber, but sometimes launches itself into the air between trees. When it does this it spreads its ribs, flattens the body, and pulls its underside in, so that it is concave. Its parachuting glide takes it some distance before it lands in another tree, resumes its normal shape, and then begins climbing again.

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Gliding reptiles of the past

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HE FOSSIL RECORD shows that almost as long as there have been lizard-like reptiles, some have taken to the air by gliding. Sometimes their adaptations are strikingly similar to the modern flying dragon, although they are not close relations. Over 250 million years ago, in what is now Madagascar, there lived Daedalosaurus. This long-tailed reptile had a series of ribs supporting wings of skin. The wingspan was about 13 inches (33 cm). The total length of the animal was 16 inches (40 cm). It probably lived in trees, and glided between them. Coelurosauravus, from a similar time, took to the air with differently-shaped gliding wings, supported by 21 pairs of bony riblike rods. Fifty million years later, the same basic design worked for Kuehneosaurus in Britain and Icarosaurus in North America. They had fewer ribs—only 10 or 11 pairs—but these supported a substantial gliding membrane. In central Asia, about the same time, two fossil reptiles had quite different methods of taking to the air. Longisquama, meaning “long scales,” had exactly that: some extremely long, flattened scales near the backbone. These scales were longer than the body. They may have folded above the back

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Present-day flying dragons, with their rib-supported wings, may seem rather odd creatures with a very specialized and unlikely body structure. However, they are by no means the first gliding reptiles.

Adapted to fly Longisquama had huge, flattened scales, which developed near the backbone, to facilitate gliding.

IN THE AIR

RIDERS AND GLIDERS

Icarosaurus This creature had a gliding mechanism supported by ribs.

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Living flying dragon

Coelurosauravus This creature had a disk-shaped gliding mechanism.

when at rest, but extended sideways to provide a gliding wing when required. Some people argue that this would not work, and suggest the structures were for display or heat regulation. Of course, structures can be dual-purpose. The living flying dragon uses the brightly-colored skin between its ribs for courtship display, as well as for gliding. Sharovipteryx had very long back legs, and a web of skin extended from the end of these down to the base of the long tail. It is not known for sure if the shorter front legs had a web too. This animal, some 10 inches (25 cm) long, must have glided a little like a paper dart. Some scientists say that its long back legs, and rather short front legs, would have made it unsuitable for tree climbing. However, legs like these are seen in some living climbing mammals that usually cling to tree trunks rather than run along branches. Sharovipteryx may well have done the same, traveling between trunks by gliding, and launching itself with a jump from the back legs. All these gliding fossil reptiles are relatively small animals— Longisquama was only about 5 inches (12 cm) long—and small, fragile animals were unlikely to be as easily fossilized as large dinosaurs were. How many other reptile gliders may there have been that we know nothing about?

Kuehneosaurus

Icarosaurus

Coelurosauravus

Daedalosaurus

Sharovipteryx

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Flying squirrels

About 50 kinds of rodents are able to sail on a gliding membrane. Most are true squirrels.

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HE SO-CALLED FLYING SQUIRRELS live in North and Central America, and in northern Asia, but are most common in south and east Asia. Quite unrelated—not squirrels at all, but related to mice—are the seven species of the “scaly-tailed flying squirrel” family, six of which are able to glide. These live in African forests. Flying squirrels have a flap of fur-covered skin at the side of the body, connected to the front and rear limbs. In a few species the membrane extends to the tail and neck. In true flying squirrels a cartilage growing from the wrist helps to support and spread the membrane. In scaly-tails, a cartilage growing from the elbow does the job. The membrane has muscles that can be contracted or relaxed to control its tension. Flying squirrels jump to launch themselves. The bigger species can glide for up to 1,500 feet (450 m). By changing limb positions and the shape of the gliding membrane, they can bank and change direction. As they reach the target tree, the tail goes down as a brake, and

Worm’s-eye view Seen from below, the extent of the flying squirrel’s gliding membrane can be appreciated.

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IN THE AIR RIDERS AND GLIDERS

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DID YOU KNOW? Why are they all fly-bynights? Do the nocturnal habits of flying squirrels protect them from dayflying predators such as hawks? They must still have to avoid owls. Some species, such as the small southern flying squirrel of the U.S., usually run round to the other side of a tree on landing. Does this protect them from a swooping owl?

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the head turns up. They land gently on the trunk, ready to run up and make another jump if needed. There is no doubt that many flying squirrels have considerable control over their flights. All the flying squirrels are nocturnal, resting in tree holes or nests during the day. They feed on nuts, seeds, flowers, fruit, leaves, and—especially the smaller species—eat insects too. Small species have a body 3 inches (8 cm) long, plus about as much tail. The largest flying squirrels can be 2 feet (61 cm) long, plus as much tail, and weigh 5 pounds (2.3 kg). Most flying squirrels have small litters of babies that develop slowly. The youngsters need to be able to glide once they are weaned. Although most kinds of flying squirrel live in warm jungles, some live in the cool, conifer forests of Asia, and some feed in conifer woodlands in the Himalayan region, sleeping during the day in high cliff caves.

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Night vision This North American flying squirrel has large eyes to help it to see where it is jumping at night.

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Pouched gliders and colugos

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OLUGOS ARE CAT-SIZED MAMMALS. Fossils are known from about 50 million years ago. Modern molecular evidence suggests that they are related, distantly, to lemurs and monkeys, but they are difficult to place on the mammal “family tree.” Colugos have the most extensive gliding membrane of any mammal. It runs from the neck down the limbs to the very tips of the fingers and toes, and right down the tail. The glide is very shallow, and they can cover more than 429 feet (130 m) between trees. They sleep by day and launch from a favorite tree as they set off for a night’s foraging. Colugos eat leaves, and have specially developed stomachs and large intestines for digesting this food. They usually hang upside down from branches. They are also good at climbing trunks. The single baby develops slowly. The mother’s gliding membrane makes a warm cradle.

As well as the flying squirrels and scaly-tails, there are two other groups of gliding mammals. Colugos live in the forests of Southeast Asia, and an assortment of marsupials have developed a gliding membrane in Australia.

Greater gliding possum A tree climber in the Australian forests, this marsupial evolved to glide in the air.

IN THE AIR RIDERS AND GLIDERS

Hanging around A colugo hangs from a branch, showing the large gliding membrane attached to its tail.

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Australia is overall a rather dry continent, but extensive areas are naturally forested. Some include the tallest trees in the world. These areas have allowed many climbers to evolve, but three families of marsupials have gone further and evolved members that take to the air. The greater gliding possum is a marsupial, but parallels the colugo in some ways. It feeds on leaves and ferments them in its gut to extract nourishment. Its gliding membrane runs from elbow to ankle, and it is a rather clumsy glider. It can be 19 inches (48 cm) long in the body, plus a slightly longer tail. The single baby is kept in the mother’s pouch for six months, and even afterward may ride on the mother’s back. Sugar gliders, as the name suggests, feed on sugars from the sap and gum of trees. They are medium-sized possums. The smallest marsupial glider is the feathertail glider. This animal is up to 3 inches (8 cm) long with a 3-inch (8 cm) tail, and rarely weighs as much as an ounce (28 g). It can glide 65 feet (20 m). It is a specialist nectar feeder, with a brush-like tip to the tongue to help lap it up. It also eats pollen and insects.

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Sweet teeth The tiny feathertail glider (above), and the sugar glider (right), are marsupials that are fond of sweet foods.

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IT’S A FACT Like other gliding mammals, the Australian marsupial gliders are all nocturnal.

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First flying insects

Meganeura (above) This giant dragonfly, dating from the Carboniferous period, was one of the largest insects known.

Euthycarcinoid Animals like this may have given rise to insects.

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N THE LATE Carboniferous period, some 300 million years ago, primitive dragonflies with a wingspan of 28 inches (70 cm), and a body to match, flew through the swamps. Already, 450 million years ago, millipede-like animals were living on land. A little later, animals we call euthycarcinoids were living. In some ways they appear halfway between millipedes and insects, and some scientists think they may have been ancestors of insects. Like insects they had three body sections—head, thorax, and abdomen—but had 11 pairs of legs, rather than three pairs like insects. Primitive insects like springtails are known from a few million years afterward. But like springtails today, they had no wings. Somewhere, though, the beginnings of insect wings were taking shape. It seems likely that insect ancestors, like crustaceans, had two parts to each limb: a lower, walking leg, and an upper “leg” that may first of all have been a gill, but which later became a kind of static sail. Perhaps these “sails” allowed the animal to skitter across a water surface, or even glide a little. When hinges and muscles were developed, it became possible to have a flapping wing. All insect wings are basically an upper and lower layer of very thin skin grown out from the body, supported by a network of tubes called veins, that provide strength and contain blood. The earliest insects, like living

Winged insects appear suddenly in the fossil record. Surprisingly, some had the biggest insect wings known, larger than those on any insect today.

Springtail Able to jump using their folded-under tail, wingless insects like this have been around for hundreds of millions of years.

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How dragonflies fly Wing

Pivot Muscles for lowering wings

Muscles for raising wings

Wing

Pivot

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IT’S A FACT In dragonflies, and some other primitive insects, each of the four wings has a separate set of muscles, and the two pairs of wings may not have a synchronized beat. The muscles act directly, pulling on the wing bases on either side of a pivot. One muscle raises the wing, the other lowers it. More “advanced” insects power the wing in a different way. But the “old-fashioned” system of the dragonfly still allows it to hover, fly fast, then catch and eat many of the more advanced types.

Supporting the wings The complex net of veins shows up well in this modern dragonfly.

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dragonflies, had wings that stuck out stiffly from the sides. By the end of the Carboniferous period, cockroaches appeared that could fold their wings in to the body, a trait typical of modern insects. It helps them to squeeze into tiny spaces and habitats they could never have entered with wings spread. The newer types of insect also cut down the “net” of veins in the wing to leave fewer, larger, and stronger supports.

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Insect wings

Like most wings, from aircraft to birds, the fundamental design of the insect wing is an airfoil. The wing is shaped so that air passing over its top surface goes farther and faster than air passing over the lower surface. This creates reduced pressure above the wing, which produces the “lift” that is the basis of flight. An insect wing is much flatter than that of an aircraft, but once in flight it is then curved into an efficient airfoil shape. Airflow over an airfoil

Forces acting on an airfoil Resultant force

Lift

Drag Direction of flying

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NSECTS DIFFER from other flying animals in that there are no muscles in their wings. In fact, in most “advanced” insects, the flight muscles are not even directly attached to the wings. The bases of the wings are pivoted between the roof of the thorax and its side wall. Muscles run from the thorax floor to its roof. When these contract, the wings are raised. Other muscles run through the thorax lengthways. These are stretched as the wings are raised, but then contract as the vertical muscles relax. The roof of the thorax arches upward, and the wing beats downward. Although the muscles powering flight are not attached to the wing, in many insects small muscles adjust the extent to which wings are angled.

How insects fly On the upstroke, the roof of the thorax is pulled down by vertical muscles. Longitudinal muscles then relax (left). On the downstroke, the vertical muscles relax, and the longitudinal muscles begin to shorten (right).

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IT’S A FACT Our muscles (and those of insects such as locusts) require an electrical signal from a nerve each time they contract, but in many insects, a single nerve impulse will set off rhythmic contractions and relaxations in the flight muscles. Only intermittent signals are needed to keep the pattern going. A fly may beat its wings at 120 beats per second, but only needs three signals per second to keep this going.

Downstroke Upstroke

Cross-section (above) The thorax of a flying insect is shown on the downstroke (top), and the upstroke (bottom).

© DIAGRAM

Devices that store energy at the end of the wing stroke, and then provide elastic recoil that helps power the next stroke, aid flight in many insects. Parts of the thorax are made of a protein called resilin, which has rubberlike properties, so the wing springs back. In some insects, such as flies, the wing is unstable around the mid-beat position, but stable at the ends of the beat, so the wing has a tendency to “click” toward the end positions. As a result of these characteristics, beating the wings requires less power. Much remains to be found out about insect flight. The complex movements made by many insect wings in hovering, maneuvering, or in straight flight, are difficult to track and explain in aerodynamic terms. In addition, the small size of many insects means that the forces and designs that are important to flight may differ from those of a large machine such as an airplane. However, the ability to fly efficiently explains much of the success of insects, with their hundreds of thousands of known species.

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Hot flyers

Insects are usually thought of as coldblooded creatures, with a body temperature that depends on their surroundings. This is largely true but, when it comes to flying, some insects operate at surprisingly high temperatures, which they can regulate to some extent.

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HE FLIGHT MUSCLES of insects account for up to a third or more of their body weight. The individual muscle fibers are relatively big, and the muscle cells have very large mitochondria. These are the “powerhouses” in cells, where oxygen is used in respiration. Some insect flight muscles appear to use oxygen faster than any other known animal tissue. Hawk moths in flight may use oxygen 100 times faster than when they are resting. It is not so surprising, then, that some of the strongest insect flyers, such as hawk moths and bumblebees, have a high temperature 104ºF (40ºC) in their flight muscles when they are hard at work. In fact, many insects may need to warm their flight muscles up to working temperature before takeoff.

Fast flyer (above) Horse botflies are among the fastest of the flying insects.

Adapting to colder weather (right) Bumblebees have warm bodies while in flight. In cooler conditions this may be an advantage over other flying insects.

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Keeping warm Hawk moths beat their wings fast, and have furcovered bodies that help them to retain heat.

IT’S A FACT Some butterflies flap their wings only a few times per second. Hawk moths may beat their wings 90 times per second, bumblebees 130, honeybees 225, and some midges up to 1,000 times per second. Speeds are often difficult to measure. Some insects may reach 42 miles per hour (68 kmph). Honeybees can certainly travel at 16 miles per hour (25 kmph), and hawk moths and botflies at 25 miles per hour (40 kmph).

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They do this either by basking in the sunlight or vibrating the flight muscles. Bumblebees and some moths and other insects have furry scales over the thorax. These make a coat to keep heat in. On a long flight the insects may need to pump blood into their abdomens to lose heat. The flight muscles in the thorax are bathed in blood, so have quick access to fuel. In some species the blood is full of sugars. These provide instant fuel, but are used up quickly. A bee exhausts its fuel in a matter of minutes, and must constantly refuel with nectar from flowers. Some insect flyers have a store of fuel as fat. This needs to be broken down to sugars before use, but it provides very compact storage. The locust, a migratory species which stores fat, can fly long distances losing only about 1 percent of its body weight each hour.

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Big wings

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Butterflies and moths have the biggest insect wings.

IT’S A FACT Some butterflies and moths have strong patterns, often eye shapes, which they flash when alarmed. These scare off predators, such as birds.

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OTHS AND BUTTERFLIES, in particular, usually beat their wings slowly compared with other insects. Some have a rather wavering flight. On the other hand, some kinds can glide quite well, especially the larger species with broad expanses of hind wing. The front and hind wings are tied together to work as a unit. In butterflies a lobe on the front of the hind wing is held under the overlapping forewing. In moths, special bristles on the front of the hind wing hook into a catch on the front wing. Some butterflies fly long distances. Although they appear jerky flyers, many butterflies land precisely and gently on a flower head when they need to feed. The greatest precisionflying is by moths, such as hawk moths, which feed by putting their long mouthparts into a flower, and suck up nectar while still on the wing. To hover, the wing beats backward and forward almost horizontally, and is turned upside-down on the “up” stroke, so that the strengthened front edge always leads. An important feature of moth and butterfly wings is their color. This comes from the covering of tiny scales. Some hold reddish or yellow pigments, as for example in the brimstone butterfly. In other cases, colors are produced by the way light is reflected from the microscopic layers in the scales. The shimmering blues and greens of the tropical Morpho butterflies, and many others, are of this type.

Eyed hawk moth The “eyes” on the wing of the hawk moth are a protective device.

Beware of poison! Heliconiids are vividly marked in warning reds, yellows, and blacks.

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Hovering The beating wings of a moth move the air.

Flying Both the forward and backward beats of a moth’s wings produce lift.

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Linking wings A rear bristle fits under a front catch. Front wing Catch Bristle

Rear wing

Atlas moth (below) One of the largest insects, its wingspan reaches 1 foot (30 cm).

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Many temperate butterflies have wings dark above, and light below. The upper side is spread in sunlight to raise the temperature ready for flying. The more reflective lower side shows when the wing is folded above the back—the usual butterfly rest posture. Colors can have many other roles. They help butterflies recognize their own kind. Even those that appear plain to us may be colored to their own kind. White butterflies, for example, can have strong patterns in the ultraviolet section of the spectrum, which we cannot see but insects can. In some species, males and females are differently colored to help pair formation. The “blues” often have bright blue males and browner females. Colors can often provide moths and resting butterflies with superb camouflage, their colors and patterns matching the locations where they are resting. Patterns can also advertise the disgusting taste or poison content of species, such as heliconiids.

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Two wings

The true flies have reduced their wings from the usual two pairs of flying membranes, found in insects, to just a single pair— equivalent to the front wings of other insects. This characteristic of flies is recognized in the name of the group—Diptera, the “twowings.” However, the remnants of the back wings remain, and they have an important use.

Taking off During the sequence, the hoverfly’s wings beat more than 100 times per second.

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HE REAR PAIR OF WINGS on a fly is reduced to a pair of knobs on stalks. These are known as halteres. They help to control the stability of flight. They vibrate up and down with the same frequency as the real wings, but their knob-shaped ends are heavy and continue to move in the original direction for a short time after the fly changes direction. This causes strains in the insect’s cuticle (skin) near the haltere bases. These are detected by sensory cells which send information to the fly’s central nervous system so that it can make any correction necessary for keeping its balance. The halteres have sometimes been compared to a gyroscope in an aircraft. The two halteres can easily be seen on a large fly such as a crane fly (daddy longlegs) but, on the smaller flies, they may be hard to see. But they are there, even on the tiniest midge. With their halteres and wings (with a “click” mechanism to make them work efficiently), together with their fast oscillating muscles, flies are among the most sophisticated insect flyers.

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They can roll, sideslip, and dodge in the air. Many fly fast. They may be able to twist upside down in an instant to land on a ceiling. How do insects without halteres control their flight attitude? Many use a less sophisticated, but workable, system based on keeping the upper part of their eyes facing towards the light. A fly keeps the top of its head facing upward in this way. If the body goes out of alignment with the head, sensors in the neck region will signal, and the wings adjust to bring the animal back to an even keel.

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IT’S A FACT Flies, bees, and wasps are the insect groups with the fastest wingbeats, even though bees have four wings. Some flies, such as hoverflies, are very good bee mimics, protecting themselves by looking like a bee. Close inspection, though, will give them away, as they only have a single pair of wings.

© DIAGRAM

Controlling flight It is easy to see the halteres— the pair of modified wings that help to control flight—on a crane fly.

haltere

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Hidden wings

The beetles, like the flies, use just one pair of wings to power their flight.

Powering flight The beetles shown below, even the rove beetle with short wing cases, have well-developed hind wings.

Rove beetle

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N THE BEETLE’S CASE, it is the hind wings that have remained as flight membranes, and the front wings have changed function. The front pair of wings develops as a pair of wing-cases, known as elytra, that are stiffened and hard, providing an armor on the outside of the beetle’s body. The functional wings are pleated and folded, and are usually tucked up next to the body underneath the elytra. Most beetles can fly, and some fly very strongly, but we sometimes forget this because our usual view of them is of an animal walking or burrowing. When a beetle gets ready for takeoff, it lifts its wing-cases up, and swings them out from the side of its body. The real wings are then unfurled from below, and may open to give a surprisingly large surface area. Some beetles are quite bulky, and need a large flight surface to get off the ground. The process can be seen, if the eye is quick enough to follow it, when a ladybug, a type of beetle, takes off. In flight, the elytra are held out stiffly at an angle. They probably give some lift to the animal as it flies, but the rear wings do all the work of flapping. A few beetles, such as the

Soldier beetle

Cockchafer

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Cockchafer in flight These are slow and clumsy flyers, often attracted to the brightness of house lights.

STRANGE BUT TRUE The glowworm is an unusual beetle. The male has both wings and elytra like a normal beetle, and flies at night in search of females. The female is completely earthbound, having neither wings nor elytra. She has a rather grublike appearance, and produces a glow of light from an organ at the end of the abdomen. This allows the flying male to locate her in the grass.

Male

Female

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rose chafer, may be able to spread their wings and fly with the elytra kept in the closed position, but this is unusual. In most beetles the elytra fold down to cover the whole body when not flying. In a few cases, such as rove beetles, they do not cover the whole abdomen, but the wings are always protected. In some flightless beetles, where the hind wings have disappeared, the elytra have become fused into a single shield. Generally, though, well-developed wings are beneath a pair of tough elytra.

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Evolution of pterosaurs

The pterosaurs were flying reptiles that lived alongside the dinosaurs until both became extinct 65 million years ago.

Rhamphorhynchus This particular type of pterosaur was common 150 million years ago. Its teeth suggest a diet of fish.

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“Eosuchian” Small agile reptiles like this may have been the ancestors of pterosaurs.

HE EARLIEST KNOWN pterosaurs come from about 220 million years ago, and they were already good flyers. There are no known fossils that show an intermediate stage on the way to becoming a flying reptile. Nobody can be sure which earlier group of reptiles were the pterosaurs’s ancestors. They probably came from the same basic stock that gave rise to dinosaurs, crocodiles, and lizards. Probably, by 250 million years ago, the animals that gave rise to pterosaurs were going their own specialized way. Pterosaurs’s ancestors were perhaps tree climbers and gliders in which the fingers of the hand, and the muscles of the arm, became ever more specialized for being in the air, until they started making flapping flights. The wing was made of skin, supported mainly by the arm, and especially by one enormously long finger. There are some 70 known kinds of pterosaur. As flying animals are relatively delicate, most would not have survived as fossils, and there

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IT’S A FACT The first pterosaur fossil to be discovered was a Pterodactylus. Cosimo Collini, of Mannheim Museum, described it in 1784. He sketched a beautiful drawing. Not surprisingly, apart from realizing it was not a bird, he found it difficult to guess the group of vertebrates to which it belonged. It was over 30 years before it was accepted as a kind of reptile.

Pterodactylus An early type of short-tailed pterosaur, this creature flourished 150 million years ago.

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were probably many more kinds during their 160-million-year history. The ones we know show an amazing range, from finch-size up to the largest flying animals that ever existed. Early pterosaurs were long-tailed. The pterodactyls, almost tail-less by comparison, had appeared by 155 million years ago. At the end of the Jurassic period 145 million years ago, long-tailed pterosaurs were extinct, and pterodactyls ruled the skies until their abrupt end 65 million years ago. The last were the biggest ever. With no relatives left today, it is hard to guess exactly how pterosaurs worked. How well did they fly? Were they cold-blooded or warm-blooded? What did they eat? Were they able to walk and run, or were they helpless on the ground? Scientists have argued about them for 200 years. Some answers are now known, but there are still things on which scientists have different opinions.

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Pterosaur wings

Rhamphorhynchus In pterosaurs the wing of leathery skin was supported by bone at the front edge.

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N SOME FOSSIL PTEROSAURS, a flight membrane can be seen. It ran from the tip of the A single finger, the fourth, fourth finger across to the side of the body, and took up more than half the back down the hind legs to below the knee. The length of the wing. As well wing was made of leathery skin with strengthening as this enormously fibers, and only had bones running along its front. elongated finger, pterosaurs The fourth finger had four bones (phalanges), each had three others, but they greatly elongated. They were tightly joined, so the were much smaller, with finger could not bend. A rolling joint between the claws that could be used for base of this finger and the metacarpal bones grasping. (equivalent to those in the palm of a human hand) allowed the finger as a whole to fold back to the body, with tip pointing upward when the animal was not flying. A small bone (the pteroid) stuck out at the front of the wing and could be moved where it joined the wrist. It probably helped stiffen a small flying membrane running from wrist to body in front of the arm, and change its angle when required.

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The muscles that worked the wing were in the upper part of the arm, and ran down to the breastbone. As in birds, the breastbone was large to fit these muscles, but lacked the keel found down the middle of a bird breastbone. Instead, a “crest” ran forward and downward. The upper arm bone (humerus) also had expanded areas for attachment of the powerful flight muscles. The shoulder bones were fused to increase strength. In some pterosaurs, parts of the backbone were fused, too. In contrast to the huge wings, the rear legs were small and not especially strong. In a few of the last pterosaurs they scarcely look capable of supporting the body’s weight. Pterodactylus skeleton

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IT’S A FACT Pterosaur bones were light but strong. Many large bones had air spaces inside. In the largest pterosaurs, the long bones had very thin walls. However, thin bony struts crisscrossed the interior, giving support just where the stresses on the bone required it.

Nostril Eye socket

First three fingers —small with claws

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Long metacarpals Pteroid bone

Cross-section This is a section through the length of a pterosaur bone, showing the struts and hollow spaces.

Lower arm

Pelvis

Tail

Lower leg

Ankle Foot

Pterodactylus skeleton Compared to its head and wing, the body of this creature was small.

© DIAGRAM

Fourth finger—the long “wing” finger

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Tailed pterosaurs

The earliest pterosaurs in the fossil record all had long tails.

Dorygnathus This pterosaur lived almost 200 million years ago. It had a long tail with a vane at its end.

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HE TAILS OF EARLY PTEROSAURS would have given stability to the animals as they flew. A vertical vane at the end of the tail helped with this. The first few vertebrae in the tail could move in the normal way, but the remainder (up to 40) had long bony projections that did not allow bending. This tail was a very stiff one. These creatures held their head in a line with the body. All the tailed pterosaurs had jaws with teeth. Usually these were sharp teeth of the type that are good for seizing fish. The oldest known pterosaur, known as Eudimorphodon, has two types of teeth in the jaw: larger “fangs” at the front and middle, and smaller teeth with several cusps at the back. Even so, it seems that it had a fish diet, as remains of fish have been found in the stomach region of a fossil. The teeth show wear that may have come from catching the hard-scaled fish of the time. Eudimorphodon had a wingspan of about 3 feet (1 m). Some tailed pterosaurs were larger, while others were smaller.

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Anurognathus To date, only one fossil of this short-headed species has been found, with a length little over 4 inches (18 cm).

Some types of Rhamphorhynchus had a wingspan of 5.5 feet (1.75 m), while other species of this genus had wings only 16 inches (40 cm) across. Like Eudimorphodon, specimens of Rhamphorhynchus have been found with fish remains inside. Most of this group were active flyers that flapped their wings to get into the air and fly forward. However, some of the later members of the group, such as Rhamphorhynchus, had long, narrow wings and may also have been good at soaring. Estimates suggest they were only about half the weight of a modern gull with a similar wingspan.

© DIAGRAM

Eudimorphodon skeleton An early pterosaur, with a wingspan just over 3 feet (1 m), it was airborne 225 million years ago.

IT’S A FACT Odd one out in this group is Anurognathus, a “longtailed” pterosaur in which the tail was reduced to a stump. A small animal, with long 20-inch (50 cm) wings in proportion to its body, it was probably an agile flyer. It had a short, wide, and deep head, with a big eye socket and rather peglike teeth. It is thought to have been an insect-eater that caught its food on the wing.

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Pterodactyls

Pteranodon This species had a skull nearly 6 feet (1.8 m) long, but was lightly built.

Pterodactyls may have evolved from the long-tailed pterosaurs. Their lack of a stabilizing tail suggests that a highly developed nervous system controlled their flight.

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TERODACTYLS’ heads were set at an angle to the backbone, as birds’ heads are. The jaws were elongated. In some, the teeth were very specialized. In others, teeth were absent altogether. The typical pterodactyl jaw had teeth adapted to a fish diet. Some pterodactyls were small. One early species of Pterodactylus was a delicate creature with a wingspan of only 10 inches (25 cm), which may have fed on insects as well as small fish. The early small pterodactyls were flapping, maneuverable flyers. Later pterodactyls were often large. One of them, Pteranodon, had a wingspan of 30 feet (9 m). The wing had different proportions to that of the long-tailed pterosaurs, with the “wrist” bones more elongated, and the fourth finger making up less of the wing length. The mode of flying was the same, but the larger species probably made use of soaring rather than flapping flight whenever they could. The bodies were

Gallodactylus This was an early pterodactyl with teeth at the front of the jaw only. Its wingspan reached as much as 4.5 feet (1.4 m).

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Tropeognathus (right) This large pterodactyl, with a wingspan of 20 feet (6 m), had a crest below and at the tip of its jaw.

Anhanguera (right) A flexible neck allowed this pterosaur to dip its head to fish as it skimmed over water.

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IT’S A FACT Described in 2002, a pterosaur named Thalassodromeus, lived in what is now Brazil 110 million years ago. It had a wingspan of 15 feet (4.5 m) and a skull 4.6 feet (1.4 m) long. The skull had a large narrow bony crest—just about the largest, compared to the skull, of any backboned animal. It was full of blood vessels and could have been important in heat regulation. It may have kept this pterosaur steady as it skimmed its lower jaw through the surface water to catch prey, rather like present-day skimmer birds.

© DIAGRAM

small compared to the wings. For example, Anhanguera had a wingspan 17 times greater than the length of its 9.5-inch (24 cm) body. There is little doubt that some big pterosaurs made long trips. One fossil Pteranodon died at sea at least 100 miles (160 km) from the nearest shore. Many large pterodactyls had crests on the head, sometimes over the beak, sometimes at the back of the head. Various functions have been suggested for these, including species recognition, or signaling the sex of the animal. However, in a huge, but lightly built flying machine, the surface area of the crests must have had a tremendous effect in the air. They probably worked as rudders. They may also have been useful stabilizers when the animals dipped their jaws in water while fishing on the wing.

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Pterosaur lifestyles

Most scientists agree that pterosaurs were efficient flyers. They are not so sure about how well they moved on the ground.

Dimorphodon

Tropeognathus

Eudimorphodon

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OME SCIENTISTS SUGGEST that pterosaurs walked on all fours, some that they could run on their hind legs. The top bone of the leg (femur) fitted into the hip at a wide angle, so it may have been difficult to stand upright. The three fingers on the front of the wing had sharp claws, suggesting that they climbed well. Trees or cliffs may have provided good launching pads for flight. As they were active flyers, were pterosaurs warmblooded? One or two specimens have been found that suggest that at least some of them were covered with hairlike fibers that could retain heat. An even, warm body temperature would enable them to fly at any time, without warming up for action as many reptiles have to. What were pterosaur brains like? We can know the shape and size of the brain by taking casts of the brain cavity from skull Adapting to eat (left) fossils. The brain had similarities to a The variety of jaw types in pterosaurs bird’s brain, but was smaller. The part suggests they had dealing with the sense of smell was different diets, and small, but parts dealing with vision feeding techniques. and movement coordination were well

Dsungaripterus Four legs or two? Either way, reconstructions of pterosaurs on the ground look awkward.

Pteranodon Pterodaustro

Topejara

Bipedal

Quadrupedal

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IT’S A FACT Fossil skin impressions show that some pterodactyls had a throat pouch. The two halves of the lower jaw also spread as they were opened. This provided a “fishing net” and pouch, rather like a modern pelican’s.

developed, as might be expected in a flying hunter. The usual diet for pterosaurs was probably fish, but their heads and jaws came in many shapes. Some had a large number of small teeth or, in some cases, bristles, fringing the mouth. These were probably a filtering mechanism for extracting large numbers of small prey from water. But how did they feed? Did they wade on all fours in the water? Reconstructions showing this look awkward. Perhaps pterosaurs were agile enough to filter the topmost water while in flight. Some pterosaurs may have eaten insects, and even shellfish and worms are suggested foods.

Germanodactylus Pterosaurs may possibly have hung from trees or cliffs, by their hind legs.

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Pouch

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The greatest flyer ever HE PTERODACTYL QUETZALCOATLUS had a long, stiff neck, with very long individual vertebrae. Toothless jaws formed a long narrow beak. A bony crest ran along the top of its head. Head and neck together were 8 feet (2.5 m) long. Until the discovery of Quetzalcoatlus in 1971, Pteranodon was the biggest pterosaur known. Many scientists have made calculations on how Pteranodon flew, and estimated its weight. It was probably only about 33 pounds (15 kg). Quetzalcoatlus must have been heavier, perhaps 180 pounds (80 kg). Even so, the weight was low compared to the wing area. It could have soared at low speed for long distances without flapping its wings. With wings stretched, it would have needed very little wind to lift it into the air. It would have found it difficult to launch itself by leaping, and it was too big to climb trees. Unlike most pterosaurs, Quetzalcoatlus was not found in rocks laid down in the sea, but in the flood plain of a slow river. Scientists speculated that it might have fed on dead animals. But landing on the ground, and standing awkwardly on hind legs and wings while trying to tear off chunks of tough meat with a toothless beak on the end of a long stiff neck, does not sound like a recipe for success. Another suggestion, that it fed on shellfish it pulled from burrows, also seems unlikely. Quetzalcoatlus probably flew slowly across water, dipping its long beak to catch fish, in typical pterosaur fashion.

The biggest flying animal was Quetzalcoatlus. Named after the Mexican god Quetzalcoatl, who took the form of a feathered snake, its remains were first found in Texas, near the Mexican border. It had a wingspan of at least 33 feet (12 m), and may even have reached 39 feet (15 m). It was as big as a small aircraft.

Quetzalcoatlus (below) This gigantic creature must have landed on the ground from time to time. How it moved, fed, or took off again, is still not known.

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Quetzalcoatlus in flight (above) This must have been a magnificent sight, with a wingspan three times the extent of any living bird.

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IT’S A FACT Quetzalcoatlus, the biggest pterosaur, is found in the last layer of rock in which dinosaur and pterosaur fossils appear before their extinction 65 million years ago. Although pterosaurs had been declining for a while, we do not know why they disappeared. Changes in climate at the end of the Cretaceous period may have meant more variable, faster winds that made slow soaring difficult. Or changes may have disrupted the plankton of the sea, and the fish that fed on them, so that pterosaurs lost their food.

Quetzalcoatlus

Human

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Pterodactyl

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Evolution of birds

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OST BIRDS FLY, and their front limbs are developed as wings, with specialized feathers. The hind limbs are used for walking, climbing, perching, or swimming. The bones are light. Some parts of the skeleton are fused together to provide strength. Instead of heavy teeth, birds have a light horny beak, adapted by shape for various diets. Birds—at least modern ones—are an easily recognized group. In recent years most scientists have surmised that birds are descended from dinosaurs, in particular, small meat-eating dinosaurs. Some grew simple feathers which may have been useful as insulation. From these developed flat feathers, typical of modern birds, that gave the possibility of flight. Arguments remain about whether animals that ran to achieve liftoff made the first flights, or whether the first birds climbed and launched themselves from the trees.

There are nearly 10,000 living bird species. Birds have a body covering of feathers, and are warm-blooded.

A baby hoatzin (above) Many of the earliest birds had claws on their wings. Modern hoatzins, when young, have wing claws that they use in climbing.

Bird relationships (right) This chart shows the degree of relationship between several bird groups on the basis of molecular studies.

Chicken

Rhea

65 million years ago

Ancestral bird

Parrot

Gull

Wren

Owl

Penguin

Diver

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Family tree of birds This chart shows the degree of relationship between several bird groups using “traditional” methods, like comparative anatomy. The chart differs considerably from the “modern” one shown on the opposite page.

Rhea

Chicken

Ancestral bird

Diver

Penguin

Gull

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IT’S A FACT Some molecular studies suggest that many modern bird groups originated farther back in time than fossils would suggest. They may also imply different relationships to those that have traditionally been recognized.

Parrot

Owl

Wren

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For many years the only known fossil that was a candidate for “first bird” status was Archaeopteryx. There was then a gap of many millions of years to the next fossils of primitive birds. In recent years, though, many new fossils of ancient birds and dinosaurs have been found that fill in some of the evolutionary gaps. They show that many types of bird or birdlike creatures lived in the past but, by 65 million years ago, all birds were essentially modern birds. Some modern groups go back to that time, or earlier, but bird evolution continued to produce new species. Because modern birds have many similarities, it is hard to draw a “family tree” to show relationships. Are similarities due to ancestry, or way of life? For example, it is possible that not all birds of prey, with their hooked beaks, are related. According to choice of defining characteristic, flamingos have been classified with storks, or with geese. Modern molecular studies may help classification, but occasionally give results that turn out to contradict anatomy.

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Archaeopteryx

Archaeopteryx was discovered in the middle of the 19th century in Solnhofen, Germany, a place renowned for fossils. Animals died in, or above, a lagoon with scarcely any oxygen. When they settled in the mud, they did not rot away quickly. The fossils they formed had fine detail preserved: insects, pterosaurs with skin impressions, and in the case of Archaeopteryx, a bird with feathers.

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HE EARLIEST KNOWN BIRD, Archaeopteryx, lived 150 million years ago. In many ways it seems a perfect link between reptiles and birds. It had wings, feathers of bird type with a vane down the middle, and asymmetrical flight feathers. There is little doubt that it could fly, but how well? This has had scientists guessing for 150 years. Its wings were well developed, but it had no keel on the breastbone as flying birds do now. It also had free fingers with large claws at the front of the wing. In modern birds, the bony tail has virtually disappeared, and the tail is just feather, but Archaeopteryx had a long bony tail clothed in feathers. It also had jaws with teeth. Archaeopteryx A reconstruction shows the creature as a tree climber (left). Its skeleton (below left) shows similarities to small dinosaurs, and its skull (below right) had numerous teeth.

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All in all, the skeleton of the crow-sized Archaeopteryx differs little from some of the small dinosaurs of the time but, as it had feathers and flew, it was recognized as the earliest known bird. Its way of life provoked plenty of discussion. It is often pictured in trees, and the claws at the front of its wings were thought to have helped it climb. (One living bird, the hoatzin, has wing claws when young and climbs well.) In this scenario, Archaeopteryx could have started flying by gliding from the trees. On the other hand, Archaeopteryx’s feet show little modification for climbing. They are like the feet of ground-living, running dinosaurs. Some people have suggested that wings were first used for catching prey (giving a use for the claws), and only later for hopping into the air and flying.

Modern bird wing Alula

Forearm

Secondaries

Primaries

Velociraptor vs Archaeopteryx There are differences in proportion, but the bones in the arms are broadly similar.

Forelimb comparisons

Velociraptor

Archaeopteryx

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Fossil This Archaeopteryx fossil was taken from Solnhofen limestone. The wing feathers (top), and tail feathers (bottom), are clearly visible.

IT’S A FACT Although some scientists argue that Archaeopteryx was just a dinosaur that happened to have feathers, there is close similarity between the arrangement, and number, of feathers in the wing of Archaeopteryx and a modern bird. This suggests that Archaeopteryx was part of the group that later gave rise to modern birds.

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Other early birds

In recent years fossil birds and birdlike dinosaurs have been discovered in Spain, Madagascar, South America, and China. They add to our knowledge, but also make us want to ask more questions about bird evolution. They show it was not a simple story.

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DINOSAUR FROM CHINA, Sinosauropteryx, was about 4 feet (1.25 m) long, walked on its hind legs, and weighed only 5 pounds (2.3 kg). Fossils show it was covered with short fibers, now interpreted as very simple feathers. It had short arms, and certainly could not fly, but its feathers may have kept it warm. Sinosauropteryx seems more “primitive” than Archaeopteryx, but it lived about 25 million years later. Caudipteryx was another small dinosaur from the same time, but this had feathers with vanes. The feathers were all symmetrical, so this was not a flyer either. These small animals show that some dinosaurs had feathers. Already, by about 125 million years ago, birds were very varied, but not identical in every way to

Sinornis This creature lived in the trees. In some ways it looks quite modern, but it still had teeth.

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modern birds. The recently discovered Jeholornis had a skeleton built for flying strongly, but it still had a long, bony tail like Archaeopteryx. Interestingly this turkeysized bird was found with 50 fossil seeds inside, showing that, even this early, some birds were adapted for seed eating. Iberomesornis was finch-sized with feet adapted for perching in trees. Its wings were better developed than those of Archaeopteryx. Eoalulavis is the earliest bird known with an alula, the extra little group of feathers at the front of the wing that is important for maneuverability in modern birds. Eoalulavis had a wingspan of 7 inches (18 cm), the size of a small finch, but food remains preserved inside show that it ate crustaceans. Eoalulavis belonged to a group of birds called enantiornithines. Fossils of this group are found in many parts of the world, dated between 130 million and 70 million years ago. Many, including Sinornis, a small treeperching bird found in China, had beaks full of teeth.

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IT’S A FACT Birds of the enantiornithine group had bones without the many blood vessels typical of modern birds. The bones seem to have grown in bursts, perhaps seasonally rather than continuously, as those of modern birds do. This may be a sign that they were not able to keep their body temperature as warm and even as modern birds can.

Iberomesornis The remains of this finch-sized creature were found in Spain.

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Legacy Various lines of ancient birds retained different “primitive features,” such as this long bony tail retained by Jeholornis.

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Feathers

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Feathers are made of a protein called keratin, the same chemical that makes the scales of reptiles, or the hair and nails of mammals. Barb

Shaft

Barbules hook on to the barbules of the next barb.

Vane

Shaft

Structure of a flight feather Flight feathers are asymmetrical. The barbs lock together to make a strong, flat surface for flight.

Quill

N A CONTOUR FEATHER a central shaft has many barbs on each side. The barbs have barbules that interlock with one another, so that the whole feather forms a flattened surface. A large feather on a big bird contains more than a million barbules. If a feather is ruffled, the bird grooms it with beak or foot, and the barbules lock together again. The structure is strong, but hollow and light. Contour feathers provide streamlining. On the wing and tail are larger versions—flight feathers—with the job of providing lift and steering. They are asymmetrical. Down feathers are loose fluffy feathers, with a short shaft that has many barbs at the end, but no connecting barbules. A layer of down under the contour feathers traps air, and provides insulation. Many young birds have down before other feathers grow. Filoplumes have a long shaft and a small downy tip. They lie in between other feathers. They have sensory cells at the base, and may monitor the lie of the feather coat. Bristles consist of a single shaft. They are often found around the eyes, sometimes forming “eyelashes,” or the base of the beak. They probably work as “feelers,” as well as giving protection.

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Feathers are sometimes bright, or may give amazing camouflage. The commonest coloring in feathers is a black pigment—melanin. It can also produce shades of brown. Reds and yellows are often from pigments that come from the bird’s food. Many colors are produced not by pigment, but by the way light is reflected from thin layers in the feather. Such physical effects cause blues, and many of the shimmering colors of feathers. Wear is one of the disadvantages of feathers. They become ragged and less effective. To counteract this, birds molt and replace their feathers, often twice a year. Growing new feathers requires a lot of food.

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STRANGE BUT TRUE Hummingbirds may have fewer than 1,000 feathers altogether. Swallows may have 1,500. Larger birds, such as eagles, can have more than 7,000. The highest known feather count was on a swan that had 25,216— over 20,000 of which were on its head and neck.

Feather types Feathers can be modified for keeping warm, to provide a flight surface, or simply as feelers.

Contour feather Down feather

Flight feather

© DIAGRAM

Filoplume

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The bird wing

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Secondaries

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Primaries

N BIRDS, the fingers are reduced to just two small ones. The thumb, at the front of the wing, can be moved separately, and has several feathers attached. It is used for slow-speed flying and maneuvering, but is normally flattened into the rest of the wing. The proportions of Alula (feathers the bones in the arm vary attached to thumb) according to species and flying style, but the Fingers forearm and the Thumb carpometacarpus (equivalent to some of the bones of the wrist and Wrist palm in humans) are elongated. The main flight Forearm feathers are primaries— attached to the hand Humerus bones—and secondaries— (upper arm attached to the forearm. bone) A bird’s wing has its bones running down its front edge.

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Scapular (shoulder) feathers

Light, toothless skull Eye socket

Box-like ribcage

IT’S A FACT A bird’s skeleton may be less than 5 percent of its total weight. Its feathers may actually weigh more.

Breastbone with keel

Tail bones Feather tail

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Active feathers Shape and spread changes in different types of flight. In this maneuver, the primary feathers twist and open. The tail feathers are spread.

Hollow bone To achieve lightness, many bird bones are hollow cylinders, reinforced with crisscrossing struts. © DIAGRAM

The primaries are most important in propelling the bird. The secondaries provide lift. The wing is an airfoil that provides lift from the flow of air over it, like an airplane wing, but a bird wing is a vastly more complicated mechanism than any aircraft wing. Bird wings propel and also steer, with some help from the tail. Birds can change the shape of their wings, and their angle to the body. Air can be allowed to flow between feathers. It is difficult to analyze exactly what happens as a bird flies. Even the feathers themselves flex and twist during flapping flight. As birds evolved, their weight reduced to fit the demands of flying. Feathers themselves are a lightweight covering. Unnecessary bones have disappeared over time. Many of those that remain are hollowed out. Air spaces run into them, and can be part of the breathing system. Struts cross their hollow interiors to provide strength. Above all, the bones are light. In the skeleton, some bones in the spine have become fused, another means of saving weight and adding strength, as ligaments and muscles that would have held them together are eliminated. Each rib has projections that overlap the next rib, strengthening the chest region. The body region of a bird forms a comparatively rigid, strong, light box, to which the wings, legs, and flexible neck are attached. The wings are above the bird’s center of gravity.

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Flight

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HERE ARE TWO main blocks of flight muscles. The larger, on the outside, is the pectoralis major. Inside is the pectoralis minor. When the pectoralis major contracts, it powers the downstroke of the wing. As it relaxes, the pectoralis minor contracts, and raises the wing. But this minor muscle is below the wing. To lift the wing, a tendon on the end of the muscle runs up through a gap in the shoulder girdle, turns over, and is fixed to the top of the humerus. The top of the shoulder girdle acts as a pulley for the tendon to run around. Both pectoralis muscles are fixed at their lower end to the breastbone. The large keel gives a big area for attachment. The pectoralis muscles are the largest in the body, about 15 percent of its weight, or up to 20 percent in strong flyers. They are efficient, with a high rate of blood flow

Along a bird’s wing lie small muscles that control the folding and flexing of joints. The muscle that powers the wing is on the chest. It works on the part of the arm closest to the body, so that heavy muscle does not need to be swung up and down with the wing.

Tendons Pectoral (chest) muscles

Outer wing light, and almost muscle-free

Wing control muscles

Muscle network Huge muscles on the chest power the bird’s wing. They are connected to the wing bones by narrow tendons.

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from the large heart, and plenty of oxygen provided by the lungs. During flight, the pectoral muscles can produce power at ten or more times the rate of most of our muscles. For fast flying, streamlining is important. The feet are tucked up to the body, and contour feathers smooth the joins of neck and body, or wing and body. Some birds are less streamlined. A crane, flying with its long legs stretched behind, is not a highly streamlined IT’S A FACT object, and does not reach high The wing area of a mute swan is about 1,050 speeds, although it is a powerful square inches (6,800 sq cm). That of a rubyflyer that can travel long distances. throated hummingbird is just 1.9 square Although flying is complex, it inches (12.4 sq cm). seems to be built into the bird, not learned. Experiments in which birds have been prevented from opening their wings until the normal time of fledging have shown that they can fly right away. Practice is not required. One diving petrel was Ruby-throated hummingbird observed to fly 6 miles (10 km) on its first emergence from a nest burrow. Wing action The pectoralis major muscle contracts during downstroke. The pectoralis minor contracts during the upstroke.

Wing bones Pectoralis minor muscle

Pectoralis major muscle

Breastbone

© DIAGRAM

Tendon over pulley

Mute swan

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Fast flyers

Many of the faster birds fly on fairly narrow, swept-back wings, as do fast aircraft. This wing shape helps to reduce drag. It contrasts with the broader, rounded shape found in many woodland birds, for which maneuverability is more important than speed in a straight line. Fast flyers have wings with a low camber that taper to a pointed tip.

Spine-tailed swift A fast flyer, but probably not as fast as commonly thought.

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HE SPEEDS OF WILD BIRDS are difficult to measure, and, under captive or controlled conditions, they may not fly as they would in the wild. The result is much dispute over maximum speeds. The highest speed for a bird in level flight is often quoted at 106 miles per hour (171 kmph) for an Asian spine-tailed swift, but many ornithologists have doubts about the accuracy of this. Likewise, although a peregrine falcon is quoted at 220 miles per hour (354 kmph) as it stooped (plunged down toward prey with wings folded), scientists think half this speed may be a more realistic maximum. It could still be the fastest bird in the air though. Many birds have an everyday cruising speed, but also another “gear” they can pull out in an emergency, to avoid danger or catch prey. Many small perching birds may be able to reach 33 mph (53 kmph) Some “normal” airspeeds accepted for birds include: Racing pigeon Woodpigeon Goose Herring gull Blue tit

44 mph (71 kmph) 38 mph (61 kmph) 34 mph (55 kmph) 24 mph (39 kmph) 18 mph (29 kmph)

Peregrine stooping Fast in level flight, a peregrine falcon picks up even more speed as it folds its wings, and plunges toward its prey.

Hobby

Griffon vulture

when they need to, but normally fly more slowly. However, noted fast flyers include some of the falcons, pigeons, ducks, and waders. Swifts, in spite of their name, do not normally fly especially fast. Large birds usually have faster flying speeds than smaller ones, but there are exceptions. Speed through the air is, of course, not the same as speed across the ground. Winds may be blowing against the bird, with it, or across it. Birds seem able to compensate automatically for moderate headwinds by flying harder.

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European sparrowhawk

High speed wings vs. woodland wings (above) The hobby has long, pointed wings designed for speed. The sparrowhawk has rounded wings. It is not as fast, but maneuverable around woods and hedges.

Wing shapes There are four basic shapes: the swallow’s wing is designed for speed; the pheasant’s is slow but powerful; the buzzard’s aids soaring; and the shearwater’s is useful for fast gliding.

Swallow

Pheasant

Rough-legged buzzard

Shearwater

© DIAGRAM

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IT’S A FACT There is more to flying than just flapping wings. Birds have to take account of wind and other air movements. Sometimes these can be used to very good effect. An African vulture was followed by a light aircraft as it covered 47 miles (76 km) at an average speed of 29 miles per hour (47 kmph) without once flapping its wings—it rode the thermal air currents to gain height.

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Hanging in the air

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HE WINGS OF SOARING BIRDS are fairly long, but also broad, with a deep camber (curve) to the upper surface. They do not sweep back to a point, but instead have a broad tip at which the individual primary feathers are shaped, so that there are spaces between their tips. These feathers are the secret behind the working of the soaring wing. A wing gives more lift if its airfoil is angled upward at the front (a high “angle of attack”), but if the angle is too great, then the airflow across the top of the wing begins to break away from the surface in eddies that cause turbulence, and a decrease in lift. At a certain point this turbulence cuts the lift so much that the bird is no longer supported, and it will stall and begin to drop. In a soaring bird, the alula (the feathers attached to the thumb) can be moved apart from the front of the main wing, leaving a small gap. Air can move through this relatively fast and flow across the main wing surface without breaking away as turbulence. The long primary feathers, with their empty slots between, act as a series of small airfoils with air moving across easily. If the wing tip were solid, turbulence would be a greater problem.

Birds of prey, such as vultures and storks, are extremely good at soaring and circling lazily in the sky with minimum effort.

Andean condor This bird has huge wings for soaring. The “slots” between the primary feathers that prevent turbulence are clearly visible in flight.

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DID YOU KNOW? Soaring does not work without rising air, so a vulture may be grounded early in the morning until the Sun has warmed the land. But, once there are thermals to ride, a vulture can cover vast distances using almost no energy. Airflow

Air flows easily over a wing at a low angle.

When a wing is at an angle to air flow, air may break away from the surface and cause turbulence.

Stork This bird can travel great distances by soaring and taking advantage of thermal air movements.

A slot provided by the alula allows the air flow to travel smoothly over the wing’s surface.

© DIAGRAM

The slotted primary feathers, and the action of the alula, help make the wing excellent for flying at slow speeds, and still give enough lift to support a large bird. The wing also provides good maneuverability. Soaring birds, such as vultures, stay airborne by finding air which is rising fast enough to counteract the slow rate at which they sink. Surprisingly, when soaring, a stork uses only one twentieth of the energy required when flapping its wings.

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Patrolling the oceans

Great shearwater This bird is skilled at gliding across the ocean’s surface on its long, pointed wings.

Albatross flight pattern The bird gains height into the wind, then turns to gain speed by losing height as it travels with the wind.

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LBATROSSES have a wingspan of 6 feet (2 m) or more. The wandering albatross can be 11 feet (3.25 m) from wingtip to wingtip. The long thin wings provide plenty of lift with a minimum of drag. Albatrosses are enormous birds, weighing up to 19 pounds (8.5 kg). In calm weather it is hard for them to become airborne. They flap their wings violently and run hard, their feet slapping on the surface as they struggle to take off. But they live in places where it is usually windy, and rarely calm. The wind at the sea’s surface, in contact with the water and waves, is greatly slowed, compared to the wind blowing above. In fact there is a gradient of speed from the sea’s surface to about 50 feet (15 m) above, where the wind is no longer slowed by the water’s influence. It is this difference in wind speeds that allows the albatross to fly as it does. The albatross flies downwind, gradually sinking through the air. Its speed is high, 35 miles per hour (55 kmph), or more. When it is nearly at the sea surface, it turns into the wind. It is traveling fast, and the wind crossing the long airfoil of its wings gives plenty of lift. The albatross starts to go up. As it does so, the wind

A few kinds of bird—shearwaters, petrels, and especially albatrosses— are amazing gliders that make use of energy from winds at sea. These birds have long, narrow wings with pointed tips, and no sign of the slots seen in slow-soaring birds.

Wind direction

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STRANGE BUT TRUE The wandering albatross has been known to cover as much as 20,500 miles (32,992 km) in 71 days.

becomes stronger and the bird’s speed slows. About 50 feet (15 m) up, it reaches a point where it is nearly stalling, and turns again to go with the wind, picking up speed as it sinks. So it continues, constantly changing kinetic energy (energy due to speed of motion) into potential energy (energy due to height) and back again. Inevitably, the albatross loses some energy to friction and heat as it moves, but the wind provides new energy. The result is that an albatross may fly for hours without flapping its wings, only making small adjustments for steering. Albatrosses spend most of the year at sea, coming to land just to mate and nest. They feed at the sea surface on krill, fish, and especially squid.

© DIAGRAM

Wandering albatross This bird spends most of its life above the ocean, gliding on the winds close to sea level.

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Hoverers

Hovering flight A hummingbird hovers, moving its wings rapidly backward and forward, and receiving lift from both strokes.

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FEW BIRDS OF PREY, such as the kestrel, are able to hover in one spot in moving air by carefully adjusting the trim of their wings, and fluttering them slightly to keep on station. The real expert hoverers, though, are the 300 or so species of hummingbird. A hummingbird can hover in exactly the same spot, or it may move backward or forward at the same height like a tiny helicopter. This is useful as it can accurately put its tubular beak into the throat of a flower to reach the nectar. The tongue is also tubelike, and can be protruded to suck nectar up. The wings of a hummingbird are unusual in that most of the length of the wing is made up of “hand” bones. The bones equivalent to those in our arm are relatively short. The bones of the wrist allow the hand to rotate through a wide arc. The wing beats almost horizontally in a slight figure of eight. As it reaches the end of a forward stroke, it is flipped over and is upside down for the backward stroke. In both directions the wing generates lift. The whole operation is so fast that the wings are just a blur, but they can be heard as the hum that gives these birds their name. The frequency of wingbeat varies from 22 per second in the larger species of hummingbird up to about 80 beats per second in some of the tiny species. In quick maneuvers, such as courtship flights, the beats per second can increase to 200 or more. Hummingbirds fly so well, and with such accuracy, that

Many birds are able to hover in one spot, even if briefly. For most, it looks like what it is—a difficult maneuver in which a large amount of energy is expended.

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Feeding A hummingbird hovers, then moves forward to insert its beak accurately into the flower.

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they have little use for walking. The small feet are reduced to just a perching role. Some hummingbirds are pugnacious birds that defend a patch of flowers from others of their own species. They fight and chase one another with enormous energy. Many have spectacular courtship flights. For example, the male Allen’s hummingbird dives toward the female from 100 feet (30 m) above in a flash of iridescent green feathers.

Wing movements (below) These movements are made by a hovering hummingbird.

IT’S A FACT Hummingbirds are amazingly maneuverable, with some reaching speeds of 45 miles per hour (72 kmph). No hummingbird is bigger than a swallow. Most are much smaller. The tiniest, the bee hummingbird, is 2.25 inches (5.7 cm) from beak tip to tail tip, with a wingspan of less than 4 inches (10 cm), and weighs one eighteenth of an ounce (1.6 g).

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Aerial courtship

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HE MALE SKYLARK flies high into the air, singing as he goes. The display marks his territory, and also attracts potential mates. Some hawks and pigeons fly in exaggerated ways as they advertise for a mate. Several types of bird show their flying prowess to impress a partner. They may fly fast, or engage in aerobatics. A pair of terns, newly courting, will rise hundreds of yards (meters) into the sky, led by the male, then glide down, tacking back and forth. Tumbling displays in which a partner slips upside down in the air to grapple the other partner’s talons are seen in birds of prey as diverse as red kites and African fish eagles. Sometimes a gift of food is exchanged in the process. The nightjars are another family that uses special courtship flights. The male common nighthawk of America dives at speed from high above toward a female on the ground, pulling out of the dive just above her. The roar of air moving through the wing feathers adds to the visual aspect of the dive. In the standard-winged nightjars of Africa the male has a specially-elongated primary feather on each wing with a long flexible shaft, and a “flag” of barbs at the end. As he circles the air above a female, the special feathers flutter above the wing, providing a visual display that can scarcely be ignored. Once he has

As animals for which flying and vision are so important, it is not surprising that many birds have special flight displays linked with courtship. In the wren, a swift aerial chase starts the courtship ritual.

Fast love The male nighthawk, an American nightjar, hurtles down toward the female on the ground as part of a courtship display.

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IT’S A FACT One kind of wading bird, the common snipe, adds mechanical sound to its display flight. The two outer feathers of the tail are built so that they vibrate at a particular airspeed. The snipe dives at a 45 degree angle with its tail fanned. At about 43 miles per hour (69 kmph), the tail feathers produce a drumming or bleating sound that carries a long way.

Energetic love Sea eagles hold each other’s talons, and also perform acrobatics as part of their courtship ritual.

won a female, the male preens off the long feathers, and they do not grow again until the next mating season. Among the wading birds there are many examples of courtship display flights. Plovers engage in twisting, tumbling, and diving flights, and many sandpipers have ritual courtship display flights.

Snipe drumming

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Finding fruit

Toco toucan This bird has an extremely large beak which it uses to gather fruit.

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N THE TROPICAL FOREST there are normally trees in flower or fruit at any time of year, but they do not occur in large groups, where birds could stay for a long time and gorge themselves. More often, they are scattered in ones and twos throughout the forest and have to be found. Many fruit-eating birds move around in flocks. Their bright colors and raucous calls help them to recognize their own kind, to stay in contact, and move swiftly to eat if any of the group finds some ripe fruit. Sometimes bands of birds of mixed species will be moving through the forest together, feeding voraciously on a particular tree until its fruit is exhausted, then moving on to the next. Many of these birds fly through or above the tree canopy, where it is easier to keep in touch than lower in the branches, and perhaps easier to spot fruit below. To feed on fruit there is no need to be a fast flyer, or to fly stealthily. It is useful to be a strong flyer to cover long distances between the fruiting forest trees, as some fruiteating parrots and fruit pigeons are. The toucans of the American tropics, and the hornbills of tropical Asia and Africa, are two families of large fruit-eating birds that show some interesting parallels, although they are not closely related. Both fly rather noisily through the forest in small flocks. Both types have enormous bills, which have several uses, one of which is to enable a large bird to sit on a branch and stretch to

Only in the tropics and subtropics are fruits available throughout the year, and it is possible for birds to be fulltime fruit-eating specialists. Birds from different families have adopted this style of life. Often they share the characteristics of striking, brightly colored plumage and of loud, carrying voices.

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IT’S A FACT Fruit trees need the birds that feed on them as much as the birds need the trees. The birds swallow fruits and digest the pulp but not the seeds within. These are regurgitated, or passed out in droppings, so spreading ready-togerminate seeds across the forest.

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Quetzal (left) The quetzal, which comes from the tropical New World, belongs to a family of fruit eaters.

pick fruit from fine twigs that would not support their weight. In spite of their size, the beaks of these birds are quite light, and do not weigh them down in flight.

Scarlet macaw (right) Parrots like this can feed on fruit, and also crack seeds and nuts open.

Fruit pigeon (above) There are many varieties of fruit pigeon. They are mostly found in Southeast Asia and some Pacific islands.

© DIAGRAM

Great Indian hornbill (right) This bird eats many fruits. It has a light beak, with a horn above it.

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Catching insects

Potoo (below) This bird has a wide gape to catch insects on the wing.

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VEN BIRDS THAT FEED on grain or fruits as adults often feed their young on insects, a good source of protein. Some birds search the ground for insects. Others work their way across leaves and twigs, searching for insect prey. A large number of birds of many different families catch flying insects. A typical way of catching insects is that seen in flycatchers. These birds sit on a prominent perch with a good field of vision, and wait for flying insects to come within range. Then they take off, grab the insect on the wing, and return to the perch to eat it, before repeating the performance. Wagtails also scan the air from a favorite perch, or even jump into the air from the ground to pursue prey. This scanning, catching, and retrieving technique is shared by many of the world’s birds,

Insects are the most common food of birds. The evolution of modern birds may partly be explained by adaptation to feeding on the numerous types of modern insects that developed with flowering plants.

Flycatcher (left) This bird intercepts insects, then takes them back to a perch to eat.

Tody (right) This bird bears the pointed beak typical of insect eaters.

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Bee-eater This bird pursues dangerous prey.

including the jacamars of South America and the todies of the Caribbean. The shrikes employ a version of this technique, sometimes catching insects in mid-air, but often flying down to the ground in pursuit of insects and small vertebrates. When they come back to the perch, they may spear the prey on a thorn, building up a small food store for later. Potoos are nocturnal birds related to nightjars that live in South America. They usually sit on a favorite tree stump perch, where their colors and patterns provide perfect camouflage during the day. At night they fly up from these perches to seize moths and beetles.

Shrike This bird makes a food store by impaling insects, or small lizards, on thorns.

IT’S A FACT Bee-eaters sometimes eat other types of insect, but their main food is, just as their name suggests, bees. They feed mainly on honeybees. The bird watches from a perch, and then flies out to intercept a bee, which it catches in its long beak, often from below. It keeps the sting well away from itself, and flies back to its perch. Here it bangs and wipes the bee’s abdomen on a branch until it has removed the sting and its venom sac. Then the bee is safe to swallow. When a bee-eater is feeding young it may have to go through this routine over 200 times every day.

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Trawling the aerial plankton

In the gathering dusk, a long-winged bird flies quietly through the air in pursuit of insects. The bird twists and turns as it follows a moth, then it catches up and its mouth closes round its prey. A nightjar has just found its first meal of the night.

Hunting for food A nightjar snaps up a moth in its large mouth.

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IGHTJARS live mainly in warm countries, but some species migrate to temperate areas in summer. They need a constant supply of insects, which they catch on the wing at night. They have soft feathers, and are usually quiet in flight. Their mouths are enormous and surrounded by bristles. They open wide to form insect traps that can engulf a large moth, or sweep up a mouthful from a swarm of mosquitoes. There is some evidence that they may be able to find food by the process of echolocation. The swallows and martins are familiar daytime flyers that find their food in the air, patrolling back and forth wherever insects congregate. Fruitful hunting grounds are often close to water. Swallows are streamlined, maneuverable flyers with a short beak and a wide gape. They catch innumerable flying insects. Different species share out the possible foods as they hunt.

Swift

Barn swallow

House martin

In areas where swallows and housemartins hunt together, the martins go for aphids and small flies, while the swallows pick off larger flies. When they are feeding young, swallows have to catch enormous numbers of insects, and squash them into a pellet that they carry to the nest. A pair brings several hundred pellets a day, with thousands of flies. Swifts, the most aerial of birds, are not related to swallows, but are closer to hummingbirds, and, like them, have tiny feet. They rarely perch, except at the nest. Swifts fly all day. At night they go high in the sky to sleep on the wing. Except when breeding, they may never settle. It has been calculated that after it fledges, a swift may travel 300,000 miles (500,000 km) before landing two years later to breed. A short bill with a wide gape helps it snatch insects on the wing for fuel.

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IT’S A FACT Like swallows, swifts feed their young with pellets of insects. But if food is scarce, the babies can get cold quickly, and lose weight for a week or so, before resuming normal growth if conditions start to improve.

Alpine swift (above) This large bird flies fast. Parties of swifts trawl the sky, calling as they go. Barn swallow (left) This bird often flies low over water to snap up insects.

© DIAGRAM

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Silent flight

Eagle owl in flight Even an eagle owl, with its 6-foot (1.8 m) wingspan, can attack prey in silence.

Owls nearly all hunt at night. They have large, well-developed eyes that give them an intelligent look, but their brainpower is not exceptional. The sense organs—their eyes and ears—are the secret of their success as hunters.

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HE EYES OF AN OWL are three times as sensitive to small amounts of light as a human’s, so they can see much better at night. Their eyes are fixed facing forward, but they have very flexible necks. The forward-facing eyes allow them to fix on prey, and judge distances well when striking. But many owls can still hunt successfully when it is too dark to see prey clearly. They rely on their ears. The ear openings are large slits at the side of the head (and nothing to do with the “ear-tufts” possessed by some owls). The facial discs of feathers seen on many owls may help focus sounds into the ears. The ears are tuned in particularly to highpitched notes such as might be produced by the squeaks and rustles of rodents. In order for the owl’s hearing to work effectively, and for the owl to sneak up on prey, it is important that the owl is quiet itself. Owls usually have large wings compared to the weight of the body. This

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Catching its prey The tawny owl watches for prey, and then homes in on it with the aid of its night vision.

makes the flight look effortless, and the wings do not have to beat fast and make noise. Another reason an owl is quiet lies in the design of the flight feathers. These have fine fringes at the edge, and a soft, velvety surface. These silence the rush of air past the feather. Most owls are silent in flight. The exceptions are the fish owls, whose underwater prey cannot hear them. Owls of open country often hunt on the wing, quartering back and forth until they locate prey. Sometimes insects are caught in flight. When birds on their roost, or rodents on the ground, are seen, an owl glides silently to its target, before seizing it with its large talons. Woodland owls, such as the tawny owl, may sit on a branch, scanning the ground below, before swooping down on a meal.

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STRANGE BUT TRUE A barn owl can line up on prey and fly to strike accurately with its talons in complete darkness.

© DIAGRAM

Owl wing feather The fringes on the feather, and its velvety surface, stop it from making a noise as it moves through the air.

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Birds of a feather

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ANY FLOCKING BIRDS are seed-eaters. Their food may be very abundant but localized. If one bird finds food, others can also make use of the food supply before the flock moves on. This may be a more efficient way of finding and utilizing food than many individuals acting independently. In a flock of insect-eating birds, some act as “beaters” for the others, flushing out prey. It may be safer living in a flock. More eyes and ears are alert for trouble, and it may be spotted faster. Each bird needs to spend less time watching, and can devote more time to feeding and other activities. A flock of birds in motion can confuse a predator, and make it more difficult to single out a target. A flock of small

About half the world’s bird species form flocks at some stage in their lives. Sometimes several kinds of bird travel in mixed flocks, as do chickadees, tufted titmice, and whitebreasted nuthatches in American woodlands. There are sometimes advantages to being in a group.

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Free spirits A flock of finches shows no particular pattern as it flies.

IT’S A FACT Small birds do not produce enough air movement in flight to make it worth other members of the flock lining up in V-formation. Their flocks are loose formations.

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Preparing to fly Barn swallows gather on telegraph wires, forming flocks ready to set off on migration.

Formation flying Large birds that form flocks, such as geese or flamingos, often travel in a V-formation to conserve energy. © DIAGRAM

birds under attack from a hawk often bunches together as it performs escape maneuvers. The birds at the center of the bunch get extra protection. A number of birds that are usually solitary form flocks at migration time. As well as giving protection, these flocks may have an advantage in that many navigators are better than one, and prevent the birds straying from the correct course. A further advantage of being in a flock is that it is possible to adopt an energy-saving flying formation. This may be especially important on migration. Geese and cranes are among the birds that fly in flocks in a V-formation. As their wings beat, these large birds create large eddies in the air. These usually represent lost energy but, if a following bird positions itself in the slipstream correctly, it can acquire extra lift and use less energy flying. On a long journey, the birds fly in relays, with a new leader taking over at intervals. Flock members share the extra effort of leading.

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Evolution of bats

Alone among mammals, bats are distinguished as the only group that truly flies.

Icaronycteris This is a fossil, dating from about 55 million years ago, of the earliest known bat. The wings, together with much of the rest of the skeleton, have been well preserved.

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ATS ARE A NUMEROUS GROUP of mammals, with nearly 1,000 species, second only to the rodents. In spite of this, they vary less in size and body form than many other mammal groups. This is because of the limits placed by their flying habits. The largest bats weigh about 2.5 pounds (1.2 kg), the smallest about one fifteenth of an ounce (2 g), but the majority are small. They do vary considerably in their feeding habits. The oldest known fossil bats come from around 55 million years ago. There are no “missing links” that show us how bats evolved. They are clearly already bats, differing from their modern counterparts only in details, such as having more teeth. The oldest were found in Wyoming, and include a remarkably complete specimen of Icaronycteris. Other fossil bats, almost as ancient, were found in Germany and Australia. Ear bones show that small bats were already using echolocation to find their way about. The larger fruit bats seem to have evolved later, with none known before about 30 million years ago. Suggestions have been made that fruit bats and typical bats may have evolved from different ancestors.

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Greater horseshoe bat

Lesser horseshoe bat

IT’S A FACT In France bat fossils belonging to five families still alive today have been found. They date from 35 million years ago. Horseshoe bats similar to those of today were already hunting through the night skies.

Long-eared bat This is a typical modern bat. However, the basic pattern of the body and wings is very ancient.

© DIAGRAM

However, the overall similarity between the two main groups of bats, and investigations into their DNA, suggest common ancestry. What was the bat’s ancestor? It was a small, nocturnal, insectivorous mammal. This is not very surprising, as most early mammals could be described this way. Certainly in both structure and chemistry, bats share characteristics with presentday insectivores, such as shrews. Perhaps some early insectivores took to climbing trees, and found it useful to launch themselves at flying prey. Perhaps a gliding stage led to true flying. Being small, bats rarely fossilize. Even the fossils that we have suggest that this distinctive group may have begun to evolve right back in the time of the dinosaurs. Like their ancestors, bats have remained nocturnal, and so avoid competition with birds, which are mostly creatures of the day.

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Bat wings

The surface of a bat’s wing is a flexible, elastic membrane made up of two thin layers of skin. The membrane may be only a small fraction of an inch (centimeter) thick in a small bat, but it is surprisingly strong. An impressive display A greater horseshoe bat spreads its wings, showing all the bones within that support the skin.

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HE FLIGHT MEMBRANE is supported by the bones of the arm and hand, but also spreads across to the ankles. In some bats the tail is free, but in many the flight membrane joins the hind legs to the tail. Often a supporting cartilage that keeps the membrane spread sticks inward from the ankle. Within the wing membrane are small blood vessels. Embedded in it are also many elastic fibers and small muscle fibers that can help to keep it taut, or to change shape slightly in flight. A bat’s arm bones are basically similar to ours, but the finger bones are enormously elongated. Each finger (digit) may be longer than the bat’s body. The thumb (first digit) is quite short, and protrudes from the front of the wing. The second digit runs along the front of the wing to form its leading edge.

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Tail

Foot

Wrist

Patagium (flying membrane) Digit 5 Propagatium Digit 4

Thumb Bat structure This illustration shows the main physical features of a bat.

Digit 2 Digit 3

The third digit runs to the tip of the wing, and digits 4 and 5 run back across the wing’s width, the fifth digit controlling the camber of the wing. Nearer the body, the upper arm is relatively short, but the forearm long. From the wrist to the body runs a front wing membrane which is kept taut by a special muscle. Most of the bulk of the muscles that move the wing is close to the body, making the wing easier to swing back and forth. The hand muscles are reduced to nine, as opposed to 19 in a human, and also reduced to minimum bulk. Much of their length is tendon, as is that of the muscles that extend the wing. A bat is a miracle of microengineering and lightness. The fragile-looking wing membrane can repair itself following minor damage, and even broken finger bones, because they are supported in the membrane, may heal without problem.

IT’S A FACT As in birds, different wing shapes have evolved for different jobs. Fast flyers, such as the noctules or free-tailed bats, have long, narrow wings. Noctules can fly at 30 miles per hour (50 kmph). Slow-flying bats, such as long-eared, or horseshoe bats, that are good at maneuvering amid vegetation and hovering, have relatively short, broad wings.

Noctule

Long-eared

Mexican free-tailed

Greater horseshoe

© DIAGRAM

Elbow

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How well do they fly?

The wing muscles of bats differ from those of birds in several ways. Instead of the single large muscle that powers the downstroke of a bird wing, a bat uses four muscles.

Flying bats Bats adopt a variety of wing positions in flight, most of which demonstrate the flexibility of the wing membrane.

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HE UPSTROKE MUSCLES are above the wing in bats, not below as in birds. Instead of a single main muscle working the upstroke, there are several muscles, equivalent to those at the back of our shoulders. The bat’s breastbone does not need a huge keel. In those bats where it has been measured, the proportion of wing muscle to body weight is about 12 percent, as in many small birds. In some respects, a bat’s wing is better than a bird’s. There are more bones, in the fingers for example, that can be moved to alter the shape, and the skin of the wing has small muscles too. The net result is a wing that provides great maneuverability. Bats can twist and turn in ways that most birds would not manage. In general bats are not so good at outright speed. Few have been accurately measured. Just

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IT’S A FACT A bat’s heart is nearly twice as big—for the animal’s size—as those of land mammals, and the blood has a very high capacity for carrying oxygen. These are both obvious adaptations for flight. The heart rate is also high. A spear-nosed bat was measured with a heart rate of 522 beats per minute at rest, but increased this to 822 per minute in flight, and the breathing rate nearly trebled from its resting 180 breaths per minute.

41 miles per hour (65 kmph) is about the fastest known, but most birds of bat size are not very fast either. Many bats have a larger wing area, compared to their weight, than a typical bird. They have spare capacity over what is needed to lift their own weight. This is important for animals that sometimes carry their young with them on flights, or that catch, on the wing, prey that is larger than themselves. One American red bat was recorded, grounded, with four young clinging to her. Together they weighed twice as much as she did. She could not take off, but had flown from elsewhere, carrying this enormous load.

© DIAGRAM

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Finding the way

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HE SOUNDS PRODUCED BY A BAT are very high, and the ones used for echolocation are beyond the normal range of human hearing. This is just as well because they are as loud as a pneumatic drill. The bat produces sounds from its larynx (voice box) that are directed out through the mouth in some species. In other species the sounds are sent out via the nose. The strange-looking flaps, spikes, “horseshoes”, and wrinkles of skin on bats’ faces, not to mention their varied earflaps, seem designed for the job of directing the sounds out in a particular direction, and gathering echoes efficiently. Bats seem to navigate almost unerringly by echolocation. They can fly around trees, twigs, and

Most bats are not blind. They can see quite well in dim light. But they can also find their way about in absolute darkness, using their sense of hearing. To do this, a bat produces a sound itself, and listens to the echo coming back from objects in front of it. Gathering echoes The ears of the brown long-eared bat are huge, and have a spike-shaped “tragus” at the base. These ears help collect and analyze echoes.

Echolocation A bat can locate tiny prey by listening to echoes of the bat’s voice bouncing back from objects. Sonar emitted by bat

Prey Echo received by bat

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other obstacles, and can distinguish tiny insects by their echo, and home in on them for food. Different species of bat have voices of different pitch, and they differ in the patterns of sound they make too. One common pattern is to send out well-spaced shouts at regular intervals, increasing the frequency to obtain more information as possible prey are sensed, and the bat homes in. Bats that feed by picking food from leaves or the ground produce quieter sounds, perhaps avoiding strong echoes from the background. Most of the echolocators are Microchiroptera. Fruit bats usually use their eyes to find their way. The exceptions are the rousette bats, which usually roost in caves. They find their way around inside by clicking their tongues and listening for the echoes. It is a much less developed system than the echolocation of insect eaters.

Mouse-tailed bat Yet another odd-looking bat face with a turned-up, piglike, nose. The dozens of variations in bat faces appear to be linked with subtle variations in echolocation.

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IT’S A FACT In 1794, an Italian called Spallanzani showed that bats could fly perfectly without using their eyes, but not if their ears were blocked. This was difficult to explain. Not until 1938 was equipment available that could demonstrate that bats produced sounds inaudible to humans, following which experiments began to show how the sounds were used.

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Bats and gnats Having a snack Food can be picked out from the tail “pouch,” and eaten in flight.

Using the wing The wing is sometimes used to flick a meal toward the mouth, or into the tail “pouch.”

Using the tail Some bats scoop up large insects in flight using the tail membrane.

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NSECTS ARE TYPICALLY CAUGHT by a bat as it flies. Most are caught by mouth, although bats will use a wing to field an insect that is escaping, and bring it back to the mouth. Many bats can form a kind of pouch from the tail and its attached flight membrane. This can be used to scoop food from the air, and is a good place to hold prey temporarily while the mouth gets a better purchase, or bites off the tastiest bit of a large item. The bat is able to rummage in its pouch while still flying. Some bats feed on large items such as moths or crickets. Others catch much smaller prey. Flying insects buzz and hum, so the bat may hear them, but it seems that no bat takes prey too tiny to be detected by its own particular echolocating system. The numbers eaten are astonishing. Pipistrelles have been known to eat 25 percent of their own weight by the time they return to roost. Sometimes these can

The earliest bats were insect eaters and modern bats still are. Unseen, they feed at night on enormous quantities of insects. Humans regard many of these insects, such as gnats and mosquitoes, as pests.

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all be caught in half an hour. A quarter of the weight of a pipistrelle equals 1,250 gnats. A roost of pipistrelles would eat literally millions of gnats in a month. As well as being adapted to eating insects of different sizes, bats hunt in different ways and places. Among European types, Daubenton’s bat often flies with shallow wingbeats close to the surface of water, collecting mayflies, gnats, and caddisflies. Pipistrelles fly fairly low, catching tiny prey with many twists and turns. Noctules fly high and comparatively straight, collecting larger prey, such as beetles and moths. Long-eared bats fly slowly around vegetation, hovering as they search for prey on the leaves.

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IT’S A FACT Most bats use regular flight paths and hunting areas. These may be close to the roost, and cover just a few hundred square yards (meters). On the other hand, free-tail bats living in Texas may fly at 25 miles per hour (40 kmph) or more from their roosting caves before feeding on moths and beetles.

© DIAGRAM

Skimming over the water Daubenton’s bat often flies low over water picking up insects, like this caddisfly rising from the surface.

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Carnivorous bats

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HE FALSE VAMPIRE BATS of the Old World are large bats. The biggest, the ghost bat, lives in Australia. It has a wingspan of 2 feet (60 cm), and head and body length of 5.5 inches (14 cm). It hangs in a tree waiting for prey, then swoops down to catch it. It feeds on mice, small marsupials, birds, bats, and reptiles. Asian and African relatives also eat a range of large prey, and sometimes enter houses to pick lizards from the walls. In the Americas, some of the larger members of the spear-nosed bat family are carnivorous, including the biggest, the spectral false vampire of South America, which has a wingspan of 3 feet (90 cm), and regularly eats small mammals and birds. It stalks grounddwelling prey before dropping on it, and biting the head with its large teeth. It also eats spear-nosed bats of a species with a 1.5-foot (45 cm) wingspan. A few species of bat specialize in fishing. The fisherman bat lives in Central and South America, and hunts above fresh water and the sea. It has long hind legs, False vampire bat Despite its name, this is not a bloodsucker, but it is a ferocious hunter.

Many bats include a selection of vertebrates in their food. There are bats that catch mice, those that catch frogs, and even some that catch other bats. A small number of species specialize in fishing.

Fisherman bat This bat detects fish living near the water surface by echolocation, focusing on the ripples they produce, and then flies low, trailing its feet in the water.

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and very long, narrow claws, which make little disturbance in the water but can strike and grab a fish up to a maximum of 3.5 inches (9 cm) long, including anchovies. The tail pouch may be used to transfer food to the mouth. Its canine teeth are large, and the upper lips form pouches that help hold a slippery fish. Its fur is short and greasy so that water is easily shed. The fishing bat Pizonyx belongs to the family of little brown bats, and lives on the Mexican coast. This also fishes by trailing its claws in the water, but the tail membrane may help as a scoop for holding little fish.

Frog-eating bat The frog-eating bat has the “spear” on the front of its nose typical of the bat family to which it belongs.

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Frog-eating bat This bat locates its prey by homing in on the call of a frog.

© DIAGRAM

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IT’S A FACT The frog-eating bat belongs to the spearnosed bat family. It can tell from a frog’s call whether it is an edible or poisonous species.

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Vampires

Vampire teeth These can shave off fur, and then make a painless incision.

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AMPIRE BATS are a maximum of 3.5 inches (9 cm) long including head and body. They have fewer teeth than other bats, but the canines and incisors Vampire bat skull are very sharp. A vampire bat flies to find a victim, but may This skull clearly shows that the vampire bat has few, land on the ground close by, but relatively large, teeth. before creeping up on all fours. Choosing a warm patch of skin (with blood vessels near the surface) the vampire makes a quick bite that opens up the skin. Blood flows, and the vampire laps it up. At the same time bat saliva dribbles into the tiny wound. It contains an anticoagulant to stop the victim’s blood clotting, so it keeps flowing. A vampire bat feeds for about a quarter of an hour, and may drink 40 percent of its own bodyweight in blood. A bat may return to feed on the same host animal several nights in succession. The loss of blood may not be particularly significant to the host, although it can be if a number of vampires feed off the same animal. The real danger from the vampire bat is that some of them carry rabies and can infect animals (and humans) that are bitten. When Europeans arrived in America 400

Blood-drinking vampires exist, but they are small bats from Central and South America. There are three species, and they feed only on the blood of warm-blooded animals. They attack their victims at night, so gently that they rarely wake and notice.

On the ground Vampire bats walk well, and approach their victims with stealth on foot.

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Vampire bat This is the face of a small, but sometimes deadly, mammal.

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STRANGE BUT TRUE Blood is easily digested, so the vampire’s digestive system is relatively simple, but the first part of the stomach is large and distensible to hold the huge meal. Vampires produce much urine to remove excess liquid from their food.

© DIAGRAM

years ago, they brought domestic mammals with them. In many areas these are now the main large mammals, and the biggest targets for vampire bites. Humans are rarely bitten. Of the three vampire species, two prefer bird blood, but the common vampire feeds on mammals. It does not need echolocation to find prey, but eyesight and sense of smell are thought to be important. Another way that vampires differ from most bats is that they are agile on the ground. They run well on all fours, with bodies high off the ground supported on feet and wrists. They can also jump.

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Fruit bats

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RUIT BATS LIVE IN THE TROPICS of Africa, Asia, Australia, and some Pacific islands. They include the largest bats, with wingspans up to 5.5 feet (1.7 m), and may weigh 2.5 pounds (1.2 kg), although some species are tiny. They have no tail. Fruit bats have flattened cheek teeth, and large ridges across the palate of the mouth against which the tongue can squash the food. In the American tropics, there are about 30 species of fruit bat, but these belong to the spearnosed bat family of Microchiroptera, although their feeding adaptations are similar to the fruit bats of the Old World. Fruit bats are all found in the tropics, the only part of the world where a constant supply of their specialized diet is certain throughout the year. The Megachiroptera see their way when they fly, but they may locate ripe fruits by smell. Adapted to feed on wild fruits in the forest, they are sometimes tempted by commercial plantations of fruit, and become pests. Fruit bats may hang in the tree where they are feeding, or sometimes carry food off to eat elsewhere. Some may even hover as they pick off pieces of fruit. The food is thoroughly chewed or crushed, but normally only the soft

The large fruit-eating bats, the Megachiroptera, are sometimes called flying foxes, although they have nothing in common with a fox except large eyes and a long smooth muzzle.

Flying fox Large eyes and a long nose are features typical of these fruit bats.

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IT’S A FACT When roosting, fruit bats wrap their wings around their bodies like a cloak. They hold their heads in a horizontal position, unlike the Microchiroptera that usually hang their heads straight down.

On the roost A roosting colony may often contain vast numbers of fruit bats.

© DIAGRAM

pulp is swallowed. Stones and seeds are spat out. Because of this, fruit bats are important in dispersing the seeds of many forest trees. The food that fruit bats swallow consists largely of sugars, which are easy to digest, and some fiber. The digestive system is fairly short and simple, and food passes through very quickly. Fruit bats are generally strong flyers. They need to be able to travel to find the fruits that are ripening, and may make use of different fruits at different times of the year. Many kinds have special roosts, often on tall trees, which may be used for years. In some cases, roosting areas may contain 100,000 bats or more. Typically, they fly some distance from the roost to feeding areas. Mothers carry their single baby for the first few weeks of life.

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Flower bats

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HE PROBLEM of getting at nectar is solved by having a long protrusible tongue that can stretch into the depths of a flower. In some flower-feeding bats, the tongue is a quarter of the length of the body. Often the tip has long papillae that turn the end into a kind of brush that is good for lapping up this food. Flower-feeding bats live in warm areas, and belong to either the Megachiroptera, or in the Americas to the spear-nosed bat family. Most are small, but they are perhaps some of the most important mammals on the planet. Without them, a whole range of plants could die out. By their feeding activities the bats pollinate those plants with flowers that open at night. Many of the flowers have a deep trumpet shape. Most tend to have anthers with large amounts of pollen. Even though the bats consume pollen, they also become coated with pollen grains as they feed, and transfer some to other flowers when they move on. In bananas, nectar flows from dusk to midnight, then stops. It is designed to tempt bats. Passionflowers make nectar from midnight to dawn. Batattracting flowers may be white or yellow, or they may be inconspicuous, relying on scent to

Some bats feed on flowers. Nectar provides a solution of easily-digestible sugars and pollen, and is rich in proteins and minerals.

Long-nosed bat This bat has a huge tongue to enable it to reach deep down into flowers.

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IT’S A FACT How important are bats as pollinators? In the Americas, bats are known to pollinate more than 500 kinds of plant. There are probably many more. Bats are also important pollinators in the Old World.

tempt the bats. They may be held clear of leaves or spines, or may be on a tree’s trunk, so that access for bats is easier. Some bats can hover as they feed on flowers. Others fly in and dip their tongues quickly as they pass. Mexican long-nosed bats usually move in flocks of two dozen or more. They all take turns at dipping into a group of flowers that one of the flock has found, then as the nectar content lowers, move on to search for another food source. Plants pollinated by bats include the agave, the source of the drink tequila, and the giant saguaro cactus, which is home to many other species of animal.

Mexican long-nosed bat This mammal feeds on the nectar of cactus flowers.

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Why migrate?

Swallow’s nest Soon the youngsters will need to find their own way on the long journey to Africa.

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OR MANY BIRDS, the most important factor making them migrate is probably not temperature, but rather the availability of food. In winter, there may not be enough insects to feed an insect-eating bird. It must move to find food. Why do these birds not stay in the tropics, with food throughout the year? There may be advantages in moving to cooler climates in summer to make use of the seasonal abundance of insects, and the long daylight hours in which to catch them. This is also a good time to reproduce. About two-fifths of the bird species of Europe and northern Asia are migratory. It has been calculated that there may be five billion birds making the trip south each year. Rather fewer are likely to return. Birds are the champion migrators in terms of numbers, and distances traveled, but other flying animals make migrations too, including a small number of insect species, and some bat species. None goes as far as the most highly Returning home After migrating to traveled birds. Argentina, a swallow The defining feature may return to the same of migration is that nest in Alaska. animals, if they survive, make return journeys each

Some animals migrate to escape winter food shortages, moving from high latitudes toward the tropics in the fall, and back again in spring.

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year. This differs from the nomadic wanderings of some animals, or the occasional mass movements, called irruptions, that may occur when animals breed in larger numbers than usual, and spread from their usual range. Birds such as waxwings and nutcrackers irrupt from northern conifer forests after a good year, but they do not make regular return journeys. Migration allows animals to move to areas of good feeding, but migration itself is enormously costly in terms of energy. It is also dangerous in terms of weather and possible starvation en route, and there is unfamiliar terrain with many predators. Some birds put on large amounts of fat, up to half their body weight, before migration. Yet they will probably arrive at their destination on the verge of starvation unless they find good feeding spots on the way.

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Traveler In a good breeding year, waxwings may spread far from their usual range.

© DIAGRAM

IT’S A FACT Wagtails were weighed before and after crossing the Sahara desert, 1,250 miles (2,000 km) from south to north. They lost 0.3 ounces (9 g) during the flight, most of the weight lost having been fat consumed in transit.

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Homing

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Homing pigeon The ability to find its way home has allowed it to be used for carrying messages.

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SWALLOW is unlikely to remember all the landmarks necessary to fly to South America, and then return in the spring to the exact nest that it used the year before. Nor could an animal making its first migration have anything to remember. Much about animal migration remains to be discovered, but what is known reveals some remarkable abilities. A homing pigeon released on a bright day will immediately turn in the direction of home, and set off to fly there. On an overcast day, the immediate reaction is not so assured, but the bird usually finds its way home. It seems that a pigeon can sense its position by using the Sun as a compass. Of course, as the Sun crosses the sky every day, the pigeon also needs to know the time. It has its own built-in clock. Other birds tested have been found to have similar abilities. Daytime migrants can use the Sun as a directional cue. Many birds migrate at night, without the Sun, but they navigate using the positions of the star constellations in the sky.

To migrate, birds and other animals need to be able to navigate. In a local area, a bird may remember landmarks.

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STRANGE BUT TRUE Placing birds in a planetarium at migration time and changing the apparent “sky” above makes the birds face the way the stars suggest, not the true direction for migration.

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Birds are less sure of navigation in clouded conditions, but they still have clues they can use. Some sense polarized light or ultraviolet radiation that is not impeded by cloud. Tiny magnets attached to heads will disrupt the sense of direction of some birds, so presumably they normally get clues from the Earth’s magnetic field. Some birds may receive navigational clues from very low frequency sounds that are inaudible to us. These deep sounds are produced by winds moving over mountains, or islands, and may carry for thousands of miles (kilometers). Individual species may make use of several senses to navigate. The ability is built-in, with no learning needed. Less is known about how bats and insects navigate over long distances, but there are indications that bats may be sensitive to magnetism. Some butterflies steer by the Sun.

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Navigation Some indications suggest that bats may use magnetism as a means of navigation.

© DIAGRAM

Oilbird (right) Sonic clicks made by oilbirds help them home in on their nests in dark caves. The clicks can be recorded and played on an oscillograph (below).

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Insect migration

Most insects do not migrate in the true sense. Individuals do not move with the season, returning later to the same area. Most insect “migrations” are one-way movements of individuals. Locusts Swarming adults have heavilyspotted wings.

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OCUSTS are particular species of grasshopper that usually live solitary lives. When conditions are unusually favorable, after rains, the females lay many eggs which hatch successfully and the population density increases, with young nonflying locusts walking and feeding on the ground. They develop brighter Locusts Locusts fly strongly, but swarms colors than their solitary parents, and different behavior, can still be at the mercy of the wind as they try to find patches becoming gregarious and of vegetation on which to feed. keeping close together. Eventually the marching army of hoppers develops wings and takes to the air in vast numbers. Although a single locust eats little, the sheer numbers—literally billions in a big swarm—have a devastating effect. A major swarm in Africa in 1957 ate crops that could have fed one million people for a year. Eventually a swarm reaches a place with unsuitable conditions, and the locusts starve. They do not return to their place of origin. Many butterflies also make one-way trips. The red admiral is a common butterfly in Britain, but few survive the winter. In late summer, butterflies that fly from the

Two phases Swarming phases of some locust species show brighter colors and patterns than their “normal” sedentary relatives.

Swarming hopper

Swarming adult

Solitary hopper

Solitary adult

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IT’S A FACT Monarch butterflies are strong flyers that may migrate 1,000 miles (3,000 km). Tagged monarchs on migration flew at an average of 80 miles (129 km) per day.

Butterfly tree Thousands of monarch butterflies cluster together at their winter quarters in Mexico.

© DIAGRAM

European continent supplement their numbers. They breed in southern Europe early in the year. Successive generations move north, until a wave reaches Britain. The painted lady butterfly is another annual migrant to northern Europe. Some start from North Africa. We often do not know how far individuals travel, but in its three weeks of adult life, a cabbage white butterfly may move 190 miles (300 km) from its starting point. In Africa there are species of butterfly whose individuals move back and forth with the seasons. The best-known migrant among the butterflies is the monarch butterfly of North America. These butterflies fly south in the fall, hibernating in the southern U.S. and northern Mexico. In the spring they set out north again, and breed to produce the next generation.

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Bat migration

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ACED WITH A COLD WINTER with no insect food, bats often use a survival strategy different to that of birds. The bats find a sheltered spot, become torpid, and hibernate for much of the winter. The body temperatures and the tempo of body functions are lowered, although sometimes there are brief periods of activity in suitable weather. Bats in Britain mostly hibernate close to their summer quarters. Bats that live in areas with severe winters may migrate. Noctules, which are strong flyers, fly south 300 miles (500 km) or more in Russia in the fall. In North America, populations of red bat and hoary bat leave Canada and the northern United States in the fall, and fly hundreds of miles (kilometers) to the southern U.S., making the return trip in the spring. A different type of movement is seen in the little brown bat. Caves suitable for hibernation draw bats from a wide area to

Although bats do not rival birds in long-distance migratory habits, a number of species are known to make regular seasonal moves between areas. Often these involve sites which are important for hibernation, although some travel to special nursery sites to rear their young.

Noctule bat migration paths Tagged bats migrate surprising distances.

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spend the winter. One cave on Mount Aeolus, Vermont, IT’S A FACT houses 300,000 of these bats in winter. Ringing has Unexpected migrants shown that in summer these bats disperse over a wide are the pipistrelles, tiny area, up to 170 miles (274 km) away. Caves in Kentucky bats not noted for flying give winter shelter to the Indiana bat, that lives up to ability. When tagged, it its name by traveling over 300 miles (483 km) north in was discovered that spring. Limestone caves and quarry shafts that provide they flew from Russia to good hibernation sites are known in the Netherlands Bulgaria, Turkey, and and Denmark. They attract bats from 50 miles (80 km) Greece. Some flew or more for their winter sleep. 1,000 miles (1,600 km) Some fruit bats make seasonal movements, but each way. these are not associated with cold weather so much as with the availability of fruits, or the alternation of wet and dry seasons. For example, in the Ivory Coast, West Africa, the little collared fruit bat moves north from forested areas into the savanna as the rainy season sets in and food is becoming available, then returns to the forest later in the year. A winter home Little brown bats that hibernate in a single cave on Mt Aeolus, Vermont, disperse over a wide area across New England in summer.

Mt Aeolus Boston

© DIAGRAM

Little brown bat This small bat makes seasonal movements.

100

Bird migration

In many parts of the world, migratory species of bird outnumber those that stay put. In North America, birds of all sizes, from hummingbirds to rare whooper cranes, migrate south to avoid the winter. One of the greatest North American migrations no longer takes place. Huge flocks of passenger pigeons that blocked out the sun— around three billion birds—used to migrate, but they were hunted to extinction by 1900.

S

TUDIES OF BIRD POPULATIONS, together with ringing of individual birds, have allowed scientists to trace the routes taken by migrating birds. Some are what you might expect. Sea birds migrate over sea rather than land, and many land birds minimize their sea crossings. In North America, where many major geographical features run north–south, migrating birds tend to follow them. So there is a Pacific flyway, west of the Rockies, used by waterfowl and many land birds. The Mississippi provides another major route for blackbirds, thrushes, warblers, and shorebirds. Birds heading to Africa from Europe may choose to cross between Gibraltar and Morocco, or go around the eastern end of the Mediterranean rather than cross its full width. White storks take different routes around the Mediterranean depending on which area of Europe they are coming from. Many of the migrations seen in today’s birds probably have their origins at the end of the last Ice

Stork Toward Africa White storks travel from northern Europe to Africa via the Straits of Gibraltar, or the Middle East.

!

I N T H E A I R M I G R AT I O N

Barn swallow

Wheatear

IT’S A FACT Some species migrate from part of their summer range, but stay put in others. In North America, many birds of the mockingbird family migrate, but some remain during the northern winter. Migration routes Paths such as those followed by swallows and wheatears, are clues to thousands of years of history.

© DIAGRAM

Age. As the ice melted, the birds could expand their summer feeding range, but still returned to safe warm areas during the northern winter. Gradually, the summer feeding areas became farther and farther away. Some birds found new winter homes directly south of their new range. Swallows, for example, probably originated in Africa, but are found in summer over much of the Northern Hemisphere. Now North American barn swallows migrate to South America. Some birds that have spread over an enormous summer range still make extraordinary journeys back to their origins in winter. Wheatears that breed in Alaska make their way back across the whole of Asia into Africa for winter. Wheatears from Greenland and eastern Canada fly to Europe as they move to Africa, along with European individuals. The two routes taken from the two sides of North America almost certainly coincide with the two ways wheatears colonized that continent. Willow warblers from Alaska also make a long migration to Africa.

101

102

The greatest journeys

World traveler The Arctic tern probably makes the longest migration of all, traveling all the way from the Arctic to the Antarctic in the space of a single year, a distance of 22,000 miles (35,000 km).

S

WALLOWS, traveling to southern Africa or Argentina, can fly 7,000 miles (11,000 km) in each direction. But these are not the longest distances traveled by migrating birds. The Arctic tern breeds in the Northern Hemisphere, around the Arctic Circle. In the northern winter it goes to the other end of the Earth, at the edge of the Antarctic. An individual can spend almost its whole life in daylight. The distance covered on migration can be 22,000 miles (35,400 km) a year. This is recognized as the longest migration of all, but wheatears traveling from Africa to Alaska must make nearly as long a journey. The Arctic tern flies over the sea on migration, and the wheatear mostly over land, so they remain in their own element. Some birds migrate across hostile areas. Golden plovers from Alaska fly to Hawaii on migration, crossing more than 1,900 miles (3,000 km) of sea without the chance to rest. New Zealand cuckoos fly 1,000 miles (1,600 km) or more across the sea to tropical Pacific islands. Some wheatears from Greenland, instead of choosing a route

Many tiny birds that migrate from Europe fly 5,500 miles (9,000 km) by their journey’s end. They repeat this distance twice a year as long as they live.

Arctic tern



I N T H E A I R M I G R AT I O N

103

!

IT’S A FACT Migrants go high as well as far. Small birds on migration may fly at 19,500 feet (6,000 m) or more. At some points they cross mountain ranges, usually choosing passes that give an easy route. Some birds go over the top. Bar-headed geese cross the Himalayas as they migrate between India and their central Asian breeding grounds, and sometimes fly higher than Mount Everest. Ruby-throated hummingbird Breeding range Winter range

Bar-headed goose

© DIAGRAM

hopping from Iceland to Britain, go straight across the sea from Greenland to Spain on their way to Africa. This means crossing 1,900 miles (3,000 km) of sea, and implies three days of nonstop flying, unless tailwinds help the birds along. A headwind slowing the bird on such a flight could be fatal. The American blackpoll warbler flies a direct migration route from the eastern U.S. across the Caribbean to South America—about 2,500 miles (4,000 km). It is known to change altitude several times as it flies, and is believed to be making use of favorable winds. Other birds probably do the same. Even among the tiny hummingbirds, amazing feats are performed on migration. The rubythroated hummingbird goes from the U.S. to the Yucatan Peninsula of Mexico in a single journey over 500 miles (800 km) of sea.

104

Timeline

Million years ago Events 5,000–4,000 4,550 Formation of the Earth 4,000–3,000 3,600 Origins of life 3,000–2,000 2,400 First organisms with a cell nucleus 2,000 “Modern” atmosphere reached 2,000–1,000 1,400 First multicellular organisms 1,000–500 560 First multicellular animals forming communities in the sea 545 Explosion of life in shallow seas; first shelled animals 500–250 417 First land animals 360 First “amphibians” 325 First reptiles 300 Primitive dragonflies Early dragonfly 295 Insects with folding wings had evolved 250–100 250 Gliding reptiles such as Daedalosaurus in existence 220 Early pterosaurs 210 First mammals 200 Longisquama, Kuehneosaurus, and first frogs in existence 155 Tailless pterodactyls had evolved 150 Archaeopteryx in existence 130 Enantiornithines in existence Archaeopteryx 125 Jeholornis in existence 100–now 100 Early moths 85 Early waterbirds 70 Enantiornithines die out 65 Biggest ever pterosaurs before extinction; only “modern” birds survive; extinction of dinosaurs 55 First insect-eating bats Pterosaur 50 Early colugos 40 First ducks 38 Early bees 35 Horseshoe bats already evolved 30 First fruit bats known Modern bird

I N T H E A I R T I M E L I N E 105

Fossils help scientists determine when different kinds of plants and animals first appeared. Era

Millions of years ago

Proterozoic Eon

2,500–543

Proterozoic periods

bacteria, simple animals, and plants exist

Paleozoic

543–490

Cambrian

sea animals without a backbone flourish

490–443

Ordovician

early fish appear

443–417

Silurian

land plants and land arthropods appear

417–354

Devonian

insects and amphibians appear

354–290

Carboniferous

reptiles and flying insects live in forests

290–248

Permian

reptiles dominate

248–206

Triassic

dinosaurs dominate, mammals appear

206–144

Jurassic

birds appear and pterosaurs flourish

144–65

Cretaceous

flowering plants appear

65–1.8

Tertiary

dinosaurs die out, mammals spread

1..8–present

Quaternary

humans dominate

Cenozoic

Main events

© DIAGRAM

Mesozoic

Period

106

Glossary

Breastbone

Contour

Drag

Elytra

abdomen The posterior part of the body that contains the intestines in a backboned animal: the rear of three body sections in insects and crustaceans. aerial In the air. airfoil An object, usually a wing, shaped so that it produces upward force when moved through the air. alula The small collection of feathers attached to the bird’s thumb. anatomy The form and structure of an animal. anthers The male parts of a flower that produce pollen. anticoagulant A substance that prevents the thickening and clotting of blood. asymmetrical Not symmetrical, see symmetrical. atmosphere The layer of air surrounding the Earth. barb The branches from the main shaft of a feather. The barbs are often divided into barbules, which interlock with hooks to give the feather its rigidity. breastbone The bone down the center of the front of the chest. cambered With a convex slope. camouflage Colored, shaped, or with behavior that helps an animal fit in with its surroundings so that it is difficult to detect. canopy The layer in a forest formed by the interlocking upper branches of trees. carpometacarpus A section of the wing in birds containing bones that are equivalent to those in the wrist and palm in humans. cast A fossil consisting of an impression of an animal in rock. cold-blooded Describes an animal unable to keep its body at a constant temperature. contour The outer shape of a body. The contour feathers of a bird round out and smooth out its shape. crustaceans Jointed-legged animals, generally aquatic, and breathing with gills. They have a tough external skeleton, and the body is usually divided into a recognizable head, thorax, and abdomen. Crustaceans include crabs, shrimps, copepods, and others. cusp A point or bump on the top of a tooth. DNA (deoxyribonucleic acid) The genetic material of animals, passed on from one generation to another. Analyzing this chemical from different animals can show similarities that indicate their relationship. drag The backward force acting on an airfoil as it travels through the air. echolocation The process some animals use to sense their surroundings by listening to the echoes of sounds produced by themselves bouncing back from objects. elytra The front wings of beetles, turned into a hard case covering the back wings.

IN THE AIR GLOSSARY

Insectivore

Ornithologist

Predator

Primaries

© DIAGRAM

filoplume A thin hairlike feather. fledging The period during which a young bird uses wings to fly for the first time. friction Resistance to motion. halteres The hind wings of flies, modified to sense position and balance. hibernate Go into a resting state for the winter. insectivore An insect eater. insectivorous Eating insects. iridescent With a rainbowlike sheen due to surface structure. jet stream A strong stream of wind at the top of the troposphere. keel A deep ridge of bone on a bird’s breastbone providing attachment for the flight muscles. keratin The material of which horn, nails, claws, and hair are made. lagoon An area of shallow water separated from the sea by a small strip of land. lift The upward force on a wing. ligament A tough strip of tissue joining two bones. marsupial One of the group of mammals that gives birth to very immature young, which are then kept in a pouch of skin on the mother for a while. melanin A black pigment. membrane A skin or sheet of tissue covering or connecting structures in a body. metacarpals Bones in the palm of the hand. nocturnal Active at night. ornithologist Someone who studies birds. ozone layer Layer of ozone high in the atmosphere that prevents much ultraviolet radiation reaching the Earth’s surface. palate The roof of the mouth. papillae Small projections on part of an animal’s body, usually rounded or nipple-shaped. pectoralis Of the chest: name given to birds’ main flight muscles. phalanges The small bones forming fingers and toes. photosynthesis Process found in plants, which trap sunlight and use it to power the production of sugars from carbon dioxide and water. pigment A chemical that produces a color. plankton Those creatures, mostly small, that live in the surface layers of the ocean and are carried by currents. predator An animal that catches and kills other animals for food. primaries The large flight feathers on a bird wing attached to the finger region.

107

108

Glossary

Secondaries

Spinnerets

Streamlined

Thorax

Wingspan

primitive Describes an early member of a group of animals, or one showing characteristics believed to be similar to those of early animals. protein A compound essential to cells for their structure and processes. rabies A disease caused by a virus that is carried by some wild animals. It can be fatal in humans if not promptly treated. Its symptoms include fear of water. ringing The fitting of numbered rings onto the legs of birds to obtain information on their travels if they are recaptured later. rodent One of a group of mammals with large gnawing teeth at the front of the mouth. Rodents include squirrels, beavers, and rats. secondaries The feathers on a bird wing that are attached in the region of the carpometacarpus. solar radiation Light and other radiation coming from the Sun. spectrum The range of a property, such as radiation, sound, etc. spinnerets The organs from which spiders produce silk. stratosphere Layer of atmosphere up to about 30 miles (48 km) above the Earth, in which temperature decreases with height. streamlined Shaped to reduce resistance to movement through water or air. symmetrical With equal parts. For example, with two sides equal (bilateral symmetry) or similar parts arranged in a ring (radial symmetry). tendon A band of fibrous tissue that joins a muscle to a bone. territory The area that an animal defends against others of its own kind. thermal A rising column of warm air. thermosphere High part of the atmosphere in which temperature increases with height. thorax The chest region; in insects, the middle of the three body sections. troposphere The lower part of the atmosphere. turbulence Type of flow which breaks up into eddies and swirls. Turbulence round a wing produces drag. ultraviolet radiation Radiation of a wavelength a little shorter than that of true light. vane A flat surface, such as the flat part of a bird’s feather made up of barbs, or the flattened rudder at the end of a pterodactyl’s tail. vertebrae The individual bones in the backbone. very low frequency Describes very low sounds beyond the range of human hearing. warm-blooded Describes an animal able to regulate its body temperature within narrow limits. wingspan The measurement from one wingtip to the other in a flying animal when the wings are fully stretched.

Websites to visit

109

There is a lot of useful information on the internet. There are also many sites that are fun to use. Remember that you may be able to get information on a particular topic by using a search engine such as Google (http://www.google.com). Some of the sites that are found in this way may be very useful, others not. Below is a selection of websites related to the material covered by this book. Most are illustrated, and they are mainly of the type that provides useful facts. Facts On File, Inc. takes no responsibility for the information contained within these websites. All the sites were accessible as of September 1, 2003. America Zoo: Dermoptera Colugo pictures and information. http://www.americazoo.com/goto/index/mammals/dermoptera.htm Atmospheric Chemistry Data & Resources: Ozone and the Atmosphere The Earth’s atmosphere, and the part played by ozone. http://daac.gsfc.nasa.gov/CAMPAIGN_DOCS/ATM_CHEM/ozone_atmosphere.html Bat Conservation International The amazing world of bats. http://www.batcon.org BBC Walking with Dinosaurs: Quetzalcoatlus A Quetzalcoatlus fact file. http://www.bbc.co.uk/dinosaurs/fact_files/volcanic/quetzalcoatlus.shtml Bird Families of The World Photographs of many bird families. http://www.amazilia.net/images/Birds/Birds.htm Bird Flight—How They Do It Online bird flight resources. http://birding.about.com/cs/flight/ The Bumblebee Pages On bumblebees. http://www.mearns.org.uk/mrssmith/bees/bees.htm

© DIAGRAM

The Development of Insect Flight On insect evolution and flight. http://hannover.park.org/Canada/Museum/insects/insects.html

110

Websites to visit

Earthlife Web: The Insects Homepage A brief guide to insects. http://www.earthlife.net/insects/six.html Ecology Asia: The Paradise Tree Snake A page devoted to a gliding snake. http://www.ecologyasia.com/Vertebrates/paradise_tree-snake.htm Flying Snake Homepage Flying snakes in action. http://www.flyingsnake.org Leaping Lizards! Pictures and information about lizards in Southeast Asia. http://www.ecologyasia.com/FOW_Pages/singapore-lizards.htm NASA, Marshall Space Flight Center; The Atmosphere A brief introduction to the atmosphere and its layers. http://liftoff.msfc.nasa.gov/academy/space/atmosphere.html NSW National Parks and Wildlife Service: Gliding Possums Marsupial gliders. http://www.nationalparks.nsw.gov.au/npws.nsf/Content/Gliding+possums/ The Pterosaur Database An online database of pterosaur scholarship. http://www.pterosaur.co.uk Smithsonian Magazine: How Squirrels Fly Flying squirrels in a wind tunnel. http://www.smithsonianmag.si.edu/smithsonian/issues01/feb01/mall_feb01.html University of Barcelona: Fossil Insects Research into fossil insects. http://www.ub.es/dpep/meganeura/5insects.htm University of Michigan, Museum of Zoology: Bird Families A scholarly listing of the bird families of the world. http://www.ummz.lsa.umich.edu/birds/birddivresources/families.html ZoomDinosaurs.com: Feathered Dinosaurs Found in China The links between dinosaurs and prehistoric birds. http://www.enchantedlearning.com/subjects/dinosaurs/news/Feathered.shtml

Index

111

A

D

air 7 airflow over birds’ wings 57 albatrosses 58–59 Anhanguera 37 Anurognathus 35 aphids 8, 69 Archaeopteryx 43–45 Arctic terns 102 atmosphere 6–7

Dorygnathus 34 dragonflies 19, 27

glow-worms 29 golden plovers 102 great shearwaters 58

E

H

echolocation 80–82 elytra 28–29 Eoalulavis 47 Eosuchian 30 Eudimorphodon 34–35 euthycarcinoid 18

B

F

bar-headed geese 103 bats 74–91 carnivorous 84–85 migration of 98–99 vampires 86–87 bees 22–23, 27 beetles 28 bird groups 42–43 blackpoll warblers 103 brine shrimps 8 butterflies 23–25, 96–97

feathers 48–51 finches 72 fish-eating bats 84–85 flight muscles of birds 52–53 flight speed of birds 54–55 flocks of birds 72–73 flower bats 90–91 flycatchers 66 flying reptiles 10–12 flying squirrels 14–15 formation flying 73 frog-eating bats 85 fruit bats 88–89, 99 fruit-eating birds 64–65

Caudipteryx 46 cockchafers 29 Coelurosauravus 13 colugos 16–17 condors 56 courtship displays of birds 62–63

G Gallodactylus 36 Germanodactylus 39 ghost bats 84 gliding mammals 16–17

I Iberomesornis 47 Icaronycteris 74 Icarosaurus 13 insect-eating birds 66–67 insects, flying 18–29 irruptions 93

J Jeholornis 47

L locusts 96 long-nosed bats 91–92 Longisquama 12

© DIAGRAM

C

halteres 26 hawk moths 24 heliconiids 24–25 hibernation 98–99 hoatzins 42, 45 hobbies 55 homing 94–95 hornbills 65 horse botflies 22 hoverflies 26–27 hovering birds 60–61 hummingbirds 60–61 ruby-throated 53, 103

112

Index

M macaws 65 martins 68–69 Meganeura 18 migration of bats 98–99 of birds 92–93, 100–103 of insects 96–97 moths 23–25

N navigation by birds 94–95 nighthawks 62 nightjars 62–63, 68

O oilbirds 95 owls 70–71 ozone layer 6

P passenger pigeons 100 peregrine falcons 54 pipistrelles 82–83, 99 plankton, aerial 8–9, 68–69 plovers 63, 102

pottoos 66–67 Pteranodon 36 pterodactyls 31, 33, 36–37, 39–41 pterosaurs 7, 30–39

Q Quetzalcoatlus 40–41 quetzals 65

R Rhamphorhynchus 30, 32, 35

S sandpipers 63 sea eagles 63 shrikes 67 Sinornis 46–47 Sinosauropteryx 46 skylarks 62 snipe 63 soaring birds 56–57 solar radiation 6 sparrowhawks 55 spiders 9 springtails 18 storks 56–57, 100 streamlining 53

swallows 68–69, 73, 92, 94, 101–102 swans 49, 53 swifts 54–55, 69

T terns 62, 102 Thalassodromeus 37 thunderflies 8 todies 67 toucans 64 tree frogs 10 tree lizards 11 Tropeognathus 37

V vampire bats 86–87 vultures 55–57

W wagtails 66, 93 wheatears 101–102 willow warblers 100–101, 103 wings of bats 76–79 of birds 50–57 of insects 20–29