Bird

Bird, the only animal with feathers. All birds have feathers and most birds can fly. It is the possession of feathers, not the ability to fly, that distinguishes birds from other animals—some birds are flightless (such as the penguin, ostrich, emu, rhea, and kiwi) and some animals other than birds can fly (insects and bats).

Birds

Birds vary in size and color, but they all have feathers and wings.

There are about 9,000 known species of birds alive today, of which 700 species live in the United States and Canada. They range in size from the ostrich, which may reach a height of nearly eight feet (2.4 m) and a weight of more than 300 pounds (136 kg), to certain tropical hummingbirds, one of which is only two inches (5 cm) long and weighs less than one ounce (28 g). Birds are found on the icefields of the Arctic and Antarctic, in steaming rain forests and dry desert plateaus, on mountains, in meadows and forests, in crowded cities, and over desolate ocean waters great distances from land. Few spots on earth have not known birds.

The longest-living birds are generally large birds such as ostriches, vultures, eagles, and ravens. These birds live for many decades. Birds also live longer in captivity than in the wild.

Body of the Bird

Skeleton

The skeleton of all birds, except for flightless birds, such as the ostrich and rhea, is very lightweight. It contains fewer bones than the skeletons of most other vertebrates; many of these bones are either hollow or filled with tiny air pockets instead of bone marrow.

The skull is essentially like that of a reptile, and differs in many respects from both fish and mammal skulls. The bird’s skull is lengthened in the front into two mandibles (jaws) that form part of the bill, or beak. Each mandible can be moved independently of the other and of the rest of the skull. The mandibles are covered with a tough, horny sheath that is similar to skin. The bill is used not only in securing food, but also as a tool for building nests and for smoothing the feathers. The upper mandible contains two slits that function as nostrils.

The backbone is very rigid, with most of the vertebrae being fused (unjointed). Because of this rigidity, the backbone provides the strong support of the back and wings needed during flight. It also allows the bird to maintain an upright posture while standing. The backbone ends in a structure called the pygostyle, or tailbone, which supports the tail feathers.

The sternum, or breastbone, has a flat outer surface, called the keel, that provides a large surface area for the attachment of the wing muscles. Three bones, the scapula, coracoid, and furcula (commonly called the “wishbone”), form the pectoral, or shoulder, girdle. This structure, unique to birds, prevents the ribs and sternum from collapsing due to the powerful contractions of the breast and wing muscles during flight.

The skeletal structure of a bird’s wings is essentially the same as that of the forelimbs of other vertebrates. It consists of an upper arm bone (the humerus), two lower arm bones (the radius and ulna), wrist and palm bones (the carpals and metacarpals), and phalanges, or fingers. There are three fingers, but the index finger is the only one that is well developed. The primary flight feathers are attached here. The alula, or false wing, is an area on the thumb that consists of four small, stiff feathers. These feathers control the front edge of the wing during flight. Birds have very little flexibility in their wrists and hands because they have fewer wrist and palm bones than other vertebrates. The bones of the upper and lower arm provide areas of attachment for some of the secondary flight feathers.

In general, the bones of the lower leg and ankle of birds are proportionately smaller and have less flexibility than those of mammals. Most mammals have seven bones in the ankle, but birds have only two—the tibiotarsus and the tarsometatarsus.

The canvasback

The canvasback has webbed feet for swimming and diving.

Muscles

Birds are very muscular animals. Most of the muscles are concentrated in the breast and upper leg. The neck contains a mass of thin, stringy, interwoven muscles. The structure of this muscle mass is such that the neck is very flexible in its movements, permitting a bird to rotate its head to a greater extent than most other vertebrates.

The breast of a bird contains one of two types of skeletal muscle: red muscle or white muscle. Red muscles obtain their color from a network of capillaries that provide them with oxygen-rich blood. The muscles are composed of thin fibers that are rich in myoglobin, an oxygen-carrying compound. Oxygen is extracted from the blood and transported by the myoglobin to the muscle fibers where, by the chemical processes called metabolism, energy is released from protein, the main source of energy. Most birds have red breast muscles. Birds that are strong fliers over long distances, such as falcons, gulls, and sparrows, have very well-developed red breast muscles.

Birds of Australia and New Zealand

Birds of Australia and New Zealand vary in size and shape.

Internal Organs

The circulatory system of birds is similar to that of mammals. The bird has a four-chambered heart, but it is larger and more muscular than that of a mammal of comparable size. As a result, the circulation is more rapid and the blood pressure is higher than in most vertebrates. Birds are generally more active than mammals and have a higher rate of metabolism; they must eat large quantities of food to provide adequate energy. They also have a higher body temperature than most mammals. The body temperature ranges from 102° to 110° F. (39° to 43° C.).

A bird’s lungs are small and rigid. A complex system of air sacs is distributed throughout the body and is connected by tubes to the lungs and to some of the hollow bones. Unlike mammals, birds expel all the air from the lungs with each breath. As a result, the lungs are continuously bathed with fresh air. Birds, unlike mammals, have no sweat glands and thus cannot perspire to cool the body after strenuous exercise. Instead, cool air is distributed from the air sacs to adjacent organs, preventing them from overheating.

Sense Organs

Birds have a keen sense of sight. Their eyes are large and produce large, sharp images, especially helpful during flight. Most nocturnal birds have larger eyes than birds active during the day.

Birds that dive underwater, such as ducks, loons, and auks, have a transparent membrane (the nictating membrane) that covers the eye while the bird is submerged, allowing it to see underwater. Birds that inhabit open areas, such as hawks, terns, and swallows, have a horizontal streak across their retina. This area contains millions of densely packed visual cells. It lies parallel to the horizon when the head is held in its normal position. The horizontal streak allows for sharp scanning of the horizon without movement of the eyes or neck.

Most birds have both monocular and binocular vision. In monocular vision, the field of view of the two eyes does not overlap—each eye sees a different area. In binocular vision, the field does overlap, creating three-dimensional vision, which is important in judging distances. Binocular vision is essential for hunting fast-moving prey, and is most developed in birds with eyes located toward the front of the head, such as the owl and hawk. These birds rarely use their monocular vision, which covers only a narrow field. Monocular vision is the main form of vision in birds with eyes located on the side of the head, such as songbirds and water fowl. It allows them to see far to the side to detect predators. Since they eat slow-moving or inert objects, they require only a narrow field of binocular vision.

Birds have an acute sense of hearing. Their ears are small openings in the skull and are protected by feathers. Birds are able to hear sounds of frequencies much higher than those humans can perceive. This ability helps them locate burrowing insects and other prey that emit high-frequency sounds.

The African lammergeyer

The African lammergeyer uses its excellent vision to find carrion.

Food and Digestion

The Hornbill
The Hornbill has a large, curved bill topped with a bony casque.Shorebirds and seabirds live on fish, crustaceans, mollusks, and many other marine animals, both living and dead. Birds of the inland swamps and waterways eat frogs, fish, small mammals, seeds, and water plants.

Songbirds live mainly on insects. Many species of small perching birds feed on seeds and fruits. Birds of prey often eat smaller birds as well as reptiles and mammals. Vultures and other scavengers feed on carrion (the flesh of a carcass). Hummingbirds feed upon honey and nectar. Secretary birds eat snakes.

A bird’s digestive system is composed of the crop, gizzard, and stomach. The crop is an enlargement of the esophagus. It is a storage chamber where food remains until it is passed to the stomach. Hard foods such as seeds and nuts are softened here with mucus before entering the stomach.

All birds have two types of stomachs: a glandular stomach and a muscular stomach, or gizzard. The glandular stomach contains digestive glands that secrete enzymes to break down proteins and partially dissolve bones that have been swallowed. It is prominent in birds that eat their food whole, such as most birds of prey and fish-eaters.

The gizzard is lined with bands of muscles. It contains small stones and grit swallowed by the bird. These facilitate the grinding and crushing of food. In some birds of prey, such as owls and hawks, the gizzard traps indigestible matter, such as bones and feathers, which is expelled in the form of pellets by regurgitation.

The secretary bird

The secretary bird is a famous hunter of snakes.

Flight

A bird
A bird achieves forward motion, or thrust, by moving its wings.

The main feathers used in flight are the primary feathers, or primaries, and the secondary feathers, or secondaries. The primaries are firmly anchored to the carpals and metacarpals (the bones of the hand); the secondaries, to the ulna, or forearm. Most birds have 10 primaries and 20 secondaries on each wing.

Birds are capable of four types of flight: flapping, hovering, gliding, and soaring. Flapping flight is used for flying short distances and to gain altitude. It is also the main form of flight used during migrations. Flapping flight requires large amounts of energy but is very fast. Hovering flight is used to remain motionless over one spot. It requires more energy than flapping flight. Only a few species, such as hummingbirds, are capable of hovering flight. Gliding flight is the simplest form of flight. It requires little energy and is used to coast. Soaring flight is used by birds with large wingspans, such as eagles, vultures, and albatrosses, to maintain or increase altitude without flapping the wings. It is used over cliffs, large bodies of water, and hillsides where thermals (warm air currents) are deflected upward.

Whenever possible, birds take off into the wind. Many water birds, such as ducks and loons, paddle across the top of the water to gain momentum. Before landing, most birds glide to decrease their speed. They fan their tail, throw their body into an upright position, and beat their wings in front of their body. The legs absorb much of the impact of landing.

The bee hummingbird

The bee hummingbird is two inches long and capable of hovering flight.What Is a Flightless Bird?

As you might guess, a flightless bird is a bird that can’t fly. A penguin is a flightless bird. So is the ostrich. Other flightless birds include rheas (REE uhz), cassowaries (KAS uh wehr eez), kiwis (KEE weez), and the emu (EE myoo).

All birds have wings. But a flightless bird’s wings are usually small for its body. Flapping small wings doesn’t provide the “lift” needed to fly. Scientists believe that flightless birds used to be able to fly long ago, when their bodies were smaller. But over time, their bodies became larger even though their wings stayed the same size.

Not all flightless birds are closely related. But they do have much in common with each other and with other birds. All birds are vertebrates (VUR tuh brihtz), or animals with backbones. Birds are warm-blooded and hatch from eggs. All birds have feathers, and they have beaks instead of teeth.

Where in the World Do Flightless Birds Live?

Most flightless birds live in parts of the Southern Hemisphere. Emus are found in Australia. Rheas live in South America. Ostriches live in Africa—in both the Southern Hemisphere and the Northern Hemisphere. Some kinds of flightless birds live on open plains or in deserts. Others make their homes on islands far out at sea. Penguins spend much of their lives in the ocean.

There are 17 species, or kinds, of penguins. Different penguin species live in different places. Emperor penguins, for example, live along the icy coast of Antarctica. King penguins live along the rocky coastlines of South America and islands just north of Antarctica. Yellow-eyed penguins live off the coast of New Zealand, which is southeast of Australia. Galapagos (guh LAH puh gohs) penguins live farther north than all other penguins. They live along the shores of the Galapagos Islands, west of South America.

Bird Songs and Calls

The voice box of the bird is called the syrinx. It is located at the lower end of the trachea where the bronchi join. Sound is produced when the chest muscles compress a pair of air sacs that squeeze air from the lungs through the syrinx. This passage of air, in turn, causes the tympanic membranes, two pairs of elastic membranes, to vibrate, thus producing sound. Pitch and volume are regulated by varying the amounts of tension in the muscles supporting the syrinx. The complexity of the sound depends on the number of syrinx muscles acting on the tympanic membranes. Birds with only one or two pairs of syrinx muscles, such as ducks and geese, produce plain, simple sounds. Birds with five to nine pairs, such as songbirds, produce elaborate, complex sounds.

Birds produce two types of sounds: calls and songs. Calls are shrill and very short, usually of only four or five notes. Each species has a unique call or set of calls. They are used to signal the approach of a predator and to attract other birds to food. Songs are more complex. In most species they are sung only by the male in the spring, when they are triggered by the release of sex hormones. Songs are usually learned by the young through imitation. Bird songs are used to identify the location of the singer, to attract a mate, to establish a territory, and to warn others to stay away. Bird songs are variable even within a species. Birds living in different geographical areas develop dialects specific to their region.

The forebrain, an area in the forward part of the brain, controls song output. It expands during the mating season. It is generally larger in males than in females since males are usually the only ones to sing. The versatility and number of songs a bird can produce are proportional to the size of the forebrain.

The green-backed heron

The green-backed heron has a loud and sudden call.

Plumage and Coloring

The bird’s feathers have many purposes. They streamline the body, aiding the bird to move swiftly through the air or water. They protect it from heat or cold. Stiff, strong wing and tail feathers are essential for flight.

Coloring

In some species, the feathers of the male are brightly colored to attract a mate. Less often, the female has the bright feathers. Many birds are patterned to harmonize with their surrounding so that they will be less conspicuous to their enemies. This protective coloration is especially useful during the nesting season when the parent birds do not wish to attract attention to their nests. Most young birds are protectively colored.

Many birds are brilliantly colored, but many others have dull plumage. The peafowl is among the most colorful of birds. The golden pheasant of Asia is nearly as brilliant. The greater bird of paradise found in New Guinea has elongated flank feathers that form ornamental plumes. Colorful birds of North America include the flamingo, scarlet tanager, Baltimore oriole, bluebird, cardinal, goldfinch, and wood duck.

Birds of Australia and New Zealand

Birds of Australia and New Zealand exhibit their colors.

Molting

Molting is the periodic shedding of feathers and the growth of new ones. All birds molt at least once each year. The most complete molt comes after breeding. Some birds have partial molts in spring to take on more brilliant colors for the breeding season. Usually the wing feathers molt a few at a time, so that the bird’s flying ability is not seriously harmed. Male ducks and geese, however, shed all flight feathers at once and are unable to fly. Birds are quiet and keep to themselves during molting time, but are not particularly weak or helpless.

Some birds, such as hawks and owls, keep the same mate for life. Most birds, however, choose a new mate each year, and carry on an active and sometimes competitive courtship. Courtship functions not only in selecting a mate but also in driving away competitors, stimulating ovulation in the female, and helping members of a species to recognize each other. A male bird usually selects the nesting site and defends his territory from intruders. He attempts to attract a female with calls and songs, physical contact such as sparring with his bill, displays of bright feathers, elaborate dances, and morsels of food.

Some courtships are very elaborate. The male prairie chicken inflates large yellow air sacs on either side of his head, making a loud booming sound. As he gives this serenade, he performs a dance to attract a female.

The bowerbird of New Guinea builds an enclosure, or bower, decorated with leaves, flowers, and other materials. The male displays his feathers and dances near the bower to win the watching female.

Nesting

Most birds build some type of nest to protect the eggs and the young from harsh weather and from predators. Nests also retain heat, which promotes incubation of the eggs. Each species uses a distinctive set of nesting materials.

Some seabirds, such as the auk and guillemot, lay their eggs on a rock or the edge of a cliff without building a nest. Others, such as gulls and terns, collect piles of seaweed or grass. Grebes, coots, and rails make floating nests of reeds and rushes. Ducks, geese, and swans seek dry spots hidden among rushes or undergrowth, and build substantial nests lined with down from their own breasts. The nest of the eider duck is a source of down, which has commercial value as stuffing for pillows, quilts, and comforters and for lining winter coats.

Many wading birds, such as herons and most storks, nest in colonies, building platforms of sticks high in the trees. The colony rarely exceeds a dozen nests. Penguins, terns, and gulls, on the other hand, often nest in colonies of 100 to 1,000 nests. They use stones as nesting material.

The elf owl

The elf owl makes its nest in a hollow cactus.Woodpeckers, sapsuckers, and flickers cut holes for their nests in dead trees or old utility poles. The chimney swift builds a bracketlike nest of twigs and gluey saliva halfway down the inside of an unused chimney. The hummingbird builds its nest of spider webs. Certain Asiatic swifts make their nests almost entirely out of saliva, which then hardens; it is this nest that is used by the Chinese to make bird’s-nest soup.

Songbirds build many kinds of nests. The robin builds a cup-shaped nest on a tree limb. The outside is composed of coarse grasses and leaves; the inside is plastered with mud and lined with fine grasses. The Baltimore oriole weaves a hanging pouch of grass, hair, strings, and roots. The grosbeak, crossbill, goldfinch, indigo bunting, and cardinal build hemispherical nests in bushes or trees, from 5 to 30 feet (1.5-9 m) above the ground.

The tailorbird sews the edges of growing leaves together with grass. At nesting time, the male hornbill seals the female and her eggs in a hollow tree by building a wall of dried mud, leaving only a small opening for air. He attends her during the hatching period, passing food through the opening. When the young are fledged (acquire feathers), the mother breaks down the wall. The brush turkey of Australia builds a mound-shaped nest of refuse, earth, and decaying vegetation. The eggs are hatched by the heat generated by the decay process.

The American cowbird and the European cuckoo do not make nests of their own. Instead, they lay eggs secretly in the nest of another bird. The eggs are hatched and raised by unsuspecting foster parents, and often the rightful young are crowded out of the nest by the larger baby cowbirds or cuckoos. Some birds build a new nest on top of one that is found to have cowbird or cuckoo eggs in it.

Care of Eggs and Young

Birds lay one to as many as 23 eggs. Most eggs are oval but some species produce elongated or spherical eggs. Eggs of the auk and guillemot are pointed at one end and broad at the other; they roll in a circle if disturbed, preventing them from rolling off the edge of the cliff where the eggs are laid.

Most eggs have a smooth texture but some are pitted or corrugated. The eggs of ground-nesting birds have blotches, specks, and streaks that camouflage them. Eggs range in color from white to brown, green, and light blue.

Eggs must be incubated, or warmed, for 11 days to eight weeks before they will hatch. In most species the eggs are incubated by the parents, who warm the eggs by sitting on them. This may be the job of the female, of the male, or of both parents. Parents who incubate the eggs develop a brood patch, an area of bare skin on the belly. The feathers in this area fall out and the dermis of the skin becomes richly supplied with blood vessels; heat from the blood vessels is transferred from the warm brood patch to the eggs. Some birds, such as boobies and gannets, stand on the eggs, warming them with their webbed feet. Emperor penguins warm the eggs by placing them on top of their feet, where they are covered by a special fold of skin on the underside of the belly. In other species, eggs are incubated indirectly by the heat of the sun or of decaying vegetation.

While still in the shell the young, or chick, develops an egg tooth, a short, pointed horny structure at the tip of the upper mandible. It helps the chick peck its way out of the shell.

The egg tooth drops off or is worn away within 40 days after hatching.

Chicks of different species are born at different levels of maturity. They are either precocial or altricial. Precocial chicks are born covered with down and with their eyes open. They mature very rapidly. Altricial chicks, on the other hand, are born virtually helpless. They are naked at birth, blind, and too weak to stand. They usually remain in the nest for days or weeks.

Bluebirds

Bluebirds will sometimes nest in the face of a cliff.

Bird Migration

Most birds make regular seasonal journeys between wintering grounds and breeding, or nesting, grounds. These journeys are called migrations.

Birds of temperate regions migrate because of the diminished food supply brought on by winter and also to escape cold weather. Tropical birds migrate because of the diminished food supply brought on by the dry season.

Some species migrate at night, others during the day. Sparrows and most other small birds migrate at night, feeding during the day when they are safe from most of their natural enemies. Soaring birds migrate during the day when thermals, created by the heat of the sun, help them conserve energy. Some species, such as swifts and swallows, migrate during the day when flying insects, their main source of food, are active.

Migrating birds fly at different speeds. Large birds fly faster than small birds. Ducks and geese maintain an average speed of 40-50 miles per hour (64-80 km/h) while hawks and ravens fly at 22-28 mph (35-45 km/h). Most birds migrate at an altitude of 3,000 feet (900 m) or less. Some species of cranes and geese migrate at altitudes of 15,000-21,000 feet (4,600-6,400 m).

Birds, like other vertebrates, have an internal mechanism called a biological clock that controls biological rhythms, or daily and seasonal changes in the body that occur in response to changes in the environment. The nature and location of this time-keeping mechanism are not clearly understood. However, it is believed to trigger changes in the bird’s body that stimulate the urge to migrate.

Navigation

Birds use a number of methods to find their way during migration. Many use celestial navigation, a method of orienting the body to the arc of the sun, to the phase of the moon, or to the pattern of the stars. Some birds, such as pigeons, are sensitive to changes in the earth’s magnetic field and to the pull of gravity.

The senses of vision, hearing, and, in some species, smell, play important roles in navigation during migration. Birds use topographical landmarks such as mountains, river valleys, and forests to orient themselves on the migration route. They are able to detect infrasounds, low-frequency sounds that travel long distances. The pounding of the ocean surf, for example, emits infra-sounds that are detected by birds. Many birds, particularly seabirds, identify their destinations by characteristic odors. Others, such as hummingbirds and pigeons, are able to determine the position of the sun on overcast days because they can detect the ultraviolet radiation it emits.

Migration Routes

It was once believed that migrating birds from the same general area followed the same migration routes, called flyways, each year. It is now known that only certain waterfowl follow flyways; other birds take different routes each year.

Distances Covered

The length of the annual migration varies greatly with the species. The quail, cardinal, and a few other species do not migrate at all. Meadowlarks move southward less than 100 miles (160 km). Many Canadian species, such as the junco and the snow bunting, winter in the United States. Some birds from the northern United States spend the winter around the Gulf of Mexico.

The Arctic tern

The Arctic tern breeds near the North Pole and winters in the Antarctic regions.

Importance of Birds

Valuable Birds

Birds are most useful to humans as destroyers of harmful insects and as consumers of weed seeds. Predatory birds such as the hawk, eagle, and owl are essential because they keep down the populations of rats, mice, and other rodents that would otherwise devour valuable food crops. Birds also pollinate many species of flowering plants.

Guano is a valuable fertilizer obtained from the droppings of seabirds. Seeds that pass undigested through the bodies of birds fall to the ground and introduce plants into new areas. Domestic birds such as the chicken, duck, turkey, and goose contribute meat and eggs to our food supply. Game birds furnish both meat and sport. The feathers of the ostrich, pheasant, goose, and other species are used for decoration. Eiderdown, duck, goose, and chicken feathers are used to stuff pillows, quilts, and outdoor clothing.

Cockatoos

Cockatoos are large parrots native to Australia and New Guinea.

Bird Pests

In cities, the English sparrow, pigeon, and starling are often annoying because of their droppings and noise. Crows, blackbirds, starlings, and others sometimes destroy plant seedlings. Many kinds of birds attack ripe fruit; and finches, linnets, and pine siskins have been known to destroy crops of cherries, apricots, and peaches by eating the fruit buds.

Birds are carriers of the disease psittacosis (parrot fever), which can affect humans. Quarantine and inspection of imported birds have all but eliminated the disease from the United States.

Human Activities Harmful to Birds

Since about 1600, more than 100 species of birds are known to have become extinct, virtually all because of such human activities as hunting and land development. In the late 1600’s the dodo, a flightless bird found on the island of Mauritius, was killed off by hunters and by animals introduced by colonists. The passenger pigeon, one of the most common birds in North America in the early 1800’s, disappeared from the wild by 1900 because of large-scale hunting and destruction of its habitat. Other birds killed off by humans include the great auk, Labrador duck, and heath hen.

Robins, mockingbirds, and jays

Robins, mockingbirds, and jays have adapted well to the world of humans.

Are Flightless Birds in Danger?

Some flightless birds are in danger. The ostrich can no longer be found in much of its original habitat. The Galapagos penguin is in danger of becoming extinct, or dying out completely.

Flightless birds are in danger for many reasons. People have turned the feeding grounds of rheas and the ostrich into grazing lands for farms. People also hunt many flightless birds for their feathers, meat, and skin.

Oil spills from ships are a serious danger to penguins. Even a small amount of oil of this kind can hurt a penguin’s feathers and destroy its ability to stay warm in cold seas. Overfishing is also harmful to penguins. When too many fish are taken from the seas, these birds can lose much of the food they depend on.

International laws have been passed to protect many flightless birds. In addition, some of these wild animals are bred on farms.

Are Swimming Birds in Danger?

Yes, some swimming birds are in danger. But over the years, people have made great progress in protecting our wildlife. Today, many swimming birds that were once in danger are increasing in numbers.

During the 1800’s and early 1900’s, many birds were hunted for their meat and feathers. Trumpeter swans were greatly overhunted. It is believed that fewer than 70 swans were left in the United States in 1933.

Since that time, laws have been passed to protect birds and their habitats. One law, passed in 1934, is known as the Duck Stamp Act. Each year, a new stamp is issued that hunters must buy. The money raised is used to buy land and set up wildlife refuges. Today, because of laws like the Duck Stamp Act, there are about 16,000 trumpeter swans.

Are Birds of Prey in Danger?

In the United States and Mexico, the California condor is an endangered species. Here you see a baby condor that is being raised in a zoo. At the right is a condor hand puppet, which is being moved by a zoo worker. The baby thinks it is a real condor—maybe even its mother. The puppet helps the chick get used to being around condors.

In other parts of the world, some hawks, falcons, and kestrels are also endangered. Harpy eagles are rare—and are in danger of becoming extinct. The Spanish imperial eagle is on the list of endangered animals.

Owls, hawks, and other birds of prey need places to nest. They also need wide areas in which to hunt for prey. Unfortunately, many birds of prey are losing their homes. Their natural habitats are being destroyed. Conservationists are working to protect those habitats. They are also setting aside nature preserves, where the birds can live in safety.

Are Quail and Other Galliforms in Danger?

The heath hen was a kind of grouse found in parts of the United States. It became extinct, or died out, in the 1930’s, primarily because so much of its habitat was lost that it could not survive. Some other galliforms may be in danger of becoming extinct, too.

The main danger to galliforms is the activities of people. Towns and cities spread into areas that were once wild grasslands and woodlands. These habitats had made good homes for such animals as quail.

Farmers sometimes use chemicals called pesticides (PEHS tuh sydz) to kill harmful insects in their fields. But the chemicals kill all kinds of insects. Quail and other birds are sometimes unable to find enough insects to feed their hungry young.

When large mowers cut an alfalfa field or tall grass on the side of a road, the mowers can chop up the quail nests and eggs hidden in the vegetation. Many young quail are saved when the mowing of fields and roadsides is delayed until the quail nesting season is over, but this practice is not always followed.

Protection of Birds

Today, many people realize that birds should be protected from harmful human activities. There are many clubs of bird lovers dedicated to the protection of birds. Principal among these is the National Audubon Society, founded in 1905.

More than 300 areas in North America have been set aside as national wildlife refuges. No hunting or farming is permitted in these areas. National wildlife refuges were set up in 1929 by Congress. Private bird sanctuaries are maintained by organizations such as the Audubon Society. Cities and states also set aside areas where birds can breed without being disturbed by humans. Some famous bird sanctuaries are located at Pelican Island, Florida; Hawk Mountain, Pennsylvania; and Rainey Wild Life Sanctuary, Louisiana.

Another means of protection involves breeding individuals of an endangered species in captivity to build up its population. Once the group of captive birds has become well established and their wild habitat well protected, some individuals are released into the wild. This practice has helped certain species, such as the peregrine falcon, increase in numbers.

The scarlet ibis and barred antshrike

The scarlet ibis and barred antshrike are native to Central and South America.

Bird Study

The scientific study of birds is called ornithology. Bird study is also a popular hobby. No special equipment is needed for bird study, other than a notebook to list the number and kinds of birds observed and a guidebook to aid in bird identification. However, even the cheapest 4 (four magnifications) binoculars will greatly increase the pleasure. A good pair of 6 binoculars is recommended for the serious hobbyist.

Some bird watchers note the number of different species to be found in their area, and the time of year each appears. Others help take bird censuses that show the number of individuals of each species that live in a certain area. Photography of birds can be a rewarding hobby, but it demands skill and patience and requires expensive equipment.

In banding, or ringing, a numbered aluminum band is placed around the leg of a captured bird; the bird is then released. By recovering birds that have already been banded, much can be learned about migration, family habits, lifespan, and the accumulation of radioactive and toxic substances. For large birds, colored neck bands are sometimes used. In most countries, banding requires a government permit.

To track the flight of a bird, signals from a small radio transmitter attached to the bird are monitored by a person in a moving vehicle; this process is a form of telemetry. To learn about the movements of flocks of migrating birds, radio signals are transmitted into the sky and reflected off a flock. The reflected signals are monitored by a receiver on the ground and displayed on a screen; this process is a form of radar.

Tropical birds

Tropical birds come in a variety of shapes and colors.

Evolution of Birds

Most ornithologists believe that birds evolved from dinosaurs. The first known species of bird, the archaeopteryx, lived about 150,000,000 years ago. Although it had feathers and wings, it also had reptilian features, such as teeth, claws on all four limbs, and a long, bony tail. The sinornis was a type of bird that lived shortly after the archaeopteryx; it had a shorter tail and a more efficient type of wing than the archaeopteryx.

The purple-throated sunbird

The purple-throated sunbird is related to the hummingbird.

How Birds Are Classified

Birds form the class Aves of the phylum Chordata. There are two subclasses: Archaeornithes, which consists entirely of extinct birds (including the archaeopteryx); and Neornithes, which includes three superorders:

I. Odontognathae. Extinct birds that had teeth. Examples are the ichthyornis and hesperornis.

II. Impennes. This consists of only one living order, Sphenisciformes, or penguins.

III. Neognathae. There are either 28 or 29 orders to this superorder (depending on how 12 is classified). They are:

1. Struthioniformes, ostriches.

2. Rheiformes, rheas.

3. Casuariiformes, cassowaries and emus.

4. Dinornithiformes, the moas; extinct.

5. Apterygiformes, the kiwis.

6. Tinamiformes, primitive fliers. (All the birds previously listed are flightless.) An example is the tinamou.

7. Gaviiformes, freshwater diving birds with pointed bills and webbed feet.

8. Colymbiformes, or Podicipidiformes, freshwater diving birds with pointed bills and lobed feet.

9. Procellariiformes, seabirds that are strong fliers with webbed feet.

10. Pelecaniformes, pelicans and their relatives.

11. Ciconiiformes, wading birds with long necks and long legs.

11A. Phoenicopteriformes, flamingos. They are sometimes grouped with the Ciconiiformes, sometimes as a separate order.

12. Anseriformes, waterfowl.

13. Falconiformes, day-flying birds of prey.

14. Galliformes, domestic and wild fowl.

15. Gruiformes, long-legged birds with bare foreheads.

16. Diatrymiformes, large, extinct birds; found only as fossils.

17. Charadriiformes, shorebirds; live on or near water; few other characteristics in common.

18. Columbiformes, pigeons and their relatives.

19. Psittaciformes, parrots.

20. Cuculiformes, cuckoos and their relatives.

21. Strigiformes, owls.

22. Caprimulgiformes, birds with small bills but large mouths; feed on insects in flight.

23. Apodiformes (formerly Micropodiformes), swifts and hummingbirds.

24. Coliiformes, African birds that creep among tree twigs where they feed on fruit. The common name is mousebird.

25. Trogoniformes, birds with long tail coverts and beautiful plumage; live in forests.

26. Coraciiformes, brightly colored birds with short legs and long bills.

27. Piciformes, woodpeckers and their relatives.

White-eyes

White-eyes have a conspicuous white ring around each eye.Just What Are Ratites?

Ratites (RAT yts) are a large group of flightless birds. This group includes the ostrich, the emu, rheas, cassowaries, and kiwis. Like penguins, ratites are flightless. However, they are not closely related to penguins.

Like penguins and other birds, ratites have feathers. Most kinds of ratites are bigger than most kinds of penguins. And while penguins are great swimmers, no ratites can swim. Instead, ratites get around by walking and running. In fact, the ostrich can run faster than any other kind of bird.

What Are Swimming Birds?

As you can probably guess, swimming birds are birds that swim. Swans are swimming birds. So are ducks and geese. Puffins, storm-petrels, and loons are also swimming birds.

Some swimming birds, such as swans, ducks, and geese, are closely related. Others are not so closely related. Still, all swimming birds are alike in that they spend most of their lives near water.

Like all birds, swimming birds have feathers. And they have bills and feet. But the feathers, feet, and bills of swimming birds have special features for life in and near the water. Swans, for example, have waterproof feathers and webbed feet for swimming. They have flat bills for eating water plants.

What Are Galliforms?

Galliforms (GAL uh fawrmz) are the birds that scientists have grouped into a scientific order called Galliformes (gal uh FAWR meez). Like most birds, galliforms have feathers and wings. Unlike many other birds, however, galliforms live on the ground.

Quail (kwayl) are small galliforms. There are about 45 species, or kinds, of quail. Most adult quail are only 8 to 12 inches (20 to 30 centimeters) long. The heaviest quail weigh only about 8 ounces (230 grams)—the weight of a cup of yogurt

Like other galliforms, quail live on the ground and build their nests there. They hide these nests behind tall grass. Quail are able to fly. They cannot fly far, though. When quail do fly, it is usually only for a short distance and to get away from a predator, such as a fox.

Other well-known galliforms are chickens, turkeys, and pheasants (FEHZ uhntz). Because all these birds are often hunted for sport and for their meat, they are also known as game birds.

Where in the World Do Quail and Other Galliforms Live?

Quail live throughout the world. They live on grasslands and in other open habitats on all continents except Antarctica.

All galliforms, including quail, are widespread. The partridge (PAHR trihj) lives in Europe, Asia, Africa, and Australia. Grouse (grous) live in North America, Europe, and Asia. There are even a few species of galliform that live far north within the Arctic Circle.

Because many species of galliform are hunted for sport, these birds have also been introduced into areas in which they did not originally live. For example, at one time the ring-necked pheasant lived only in parts of Asia. In the late 1800’s, people brought this pheasant to Europe and North America. In many of the areas where it was introduced, the ring-necked pheasant still survives.

Why Are Some Galliforms Show-offs?

Some male pheasants have bright, showy feathers. Male turkeys spread out their fans. Male ruffed grouse also open up their fans. These are examples of male bird behaviors called displays. Another galliform with a strange display is the male Bulwer’s pheasant. This bird has bright blue areas of skin on its head, called wattles (WOT uhzl). He enlarges these wattles during a mating display.

While it seems as if these male birds are just showing off, there is a purpose behind their display behaviors. Male birds use them to attract female birds. The males with the best displays are usually the healthiest and most fit.

Female galliforms are attracted to fit males of their species because these males are often more capable of helping to raise young. In addition to being better able to raise young, healthy parents tend to produce healthy young. That is because, as with other animals, the offspring of birds share the hereditary traits of their parents.

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