Classification of birds

There are more than 8,600 species of birds alive today, compared with only about 4,500 species of mammals. Apart from the nocturnal species, most are fairly easy to observe. Probably for this reason, bird watching is an increasingly popular pastime. As a guide to the enormous variety in the world of birds, this article outlines the makeup of each of the living orders although not all taxonomists agree on the exact family groupings that constitute separate orders.

The orders of birds

Birds (class Aves) are classified into two subclasses, Archeornithes, containing the extinct Archeopteryx, and Neornithes containing all other birds. The Neornithes consists of four superorders: Odontognathae, or extinct toothed birds; Ichthyornithes, which are also extinct; and Neognathae and Impennes, which together contain all other birds. Birds are generally arranged in 28 orders and subdivided into 158 families. These orders are described in the summaries that follow. Scientists base this classification of birds on anatomy, behavior, and life history.

Order Struthioniformes. The ostrich, the largest living bird, is the single species in this order. It is a large, fast-running, flightless bird, found today in the wild only in Africa. Several other orders of birds also have evolved a flightless life style. All have breastbones that have lost the keel because there is no longer any need for attachment of flight muscles. Together with the ostrich, these birds with flat breastbones are known as the ratites (from the Latin ratis, meaning raft). All other birds, which have keel-shaped breastbones are called carinates (from the Latin carina, meaning keel). The wings of the ratites are very small and the feathers are loose and fluffy, like the down feathers of young birds. They also have strong taut legs for fast running. The ratites include the emu of Australia and the cassowaries of Australia and New Guinea (order Casuariiformes); the kiwis of New Zealand (order Apterygiformes); and the rheas of South America (order Rheiformes). Two extinct orders, the moas of New Zealand (order Dinornithiformes) and the elephant birds of Madagascar (order Aepy-ornithiformes) were also ratites.

Order Tinamiformes. The tinamous are a group of about 50 species of birds that resemble game birds, but are probably related to the rheas. Tinamous have beautifully patterned feathers that help camouflage them from predators. They are found exclusively in South America and Central America.

Order Sphenisciformes. The penguins are found only in the Southern Hemisphere, in an area that extends from near the South Pole to the Galapagos Islands on the equator off the coast of Ecuador. Like the ratites, they have abandoned flight. Superbly adapted for fast underwater swimming, their wings are paddlelike, their bodies are stocky, and their feet are webbed. They eat fishes, squids, and crustaceans and generally breed in huge colonies. Order Gaviiformes. The divers or loons are a primitive group of five species of water birds found only in the colder parts of the Northern Hemisphere. Their streamlined shape, paddlelike feet, and long necks and bills make them well equipped for catching fish under water.

The grebes (sometimes classified in their own order, Podicipediformes) are equally adapted to an aquatic life. One species has lost the power of flight completely. They are also excellent divers and are found worldwide.

Order Procellariiformes. This order consists of sea birds with long, tubular nostrils. They seldom come ashore except to breed, and all have webbed feet. Their hooked, plated bills are adapted for a diet of squids, fishes, and other marine animals. The best known family in this order is that of the large albatrosses, which are among the most impressive fliers in the bird kingdom. Other families are the shearwaters and petrels, the storm petrels, and the diving petrels.

Order Pelecaniformes. The pelicans are a group of large, fish-eating water birds and are the only birds with all four toes webbed. They are recognizable by their huge bills and highly flexible throat pouches for scooping fish out of the water. The other families are the gannets, or boobies, which dive vertically into the sea for fish from a height of 100 feet (30 meters) or more; the tropicbirds, graceful sea birds with long tail streamers; the 30 or so species of cormorants and shags, which are long-necked, long-billed, mainly black diving birds; the anhingas, or darters, which have long, snakelike necks and bodies; and the frigate birds, which are soaring birds that frequently pirate food from other sea birds.

Order Ciconiiformes. This order consists of the large, long-legged wading birds. The 50 or so species of herons, egrets, and bitterns, and the 16 species of storks in this order have daggerlike bills for spearing fish and other prey. The 30 species of ibises have slender, down-curved bills with sensitive tips for probing in mud, whereas the 6 species of spoonbills have spoon-shaped bills, which they hold open to trap small animals in the water. The 4 species of flamingos have hooked bills equipped with comblike plates that strain tiny organisms from the water pumped through them by the fleshy tongue. Flamingos hold their heads upside-down in the water to feed.

Order Anseriformes. This order is predominantly aquatic and contains more than 150 species. The birds of this order range in size from the mute swan, which weighs 33 pounds (15 kilograms) and is one of the heaviest flying birds, to the tiny ringed teal, which weighs only 10.5 ounces (300 grams). The feet are webbed, and the bill typically is broad and flattened with fine plates at the edges for straining food from the water. They breed on every continent and major island in the world except Antarctica.

Order Falconiformes. This order comprises the birds of prey. It is a large order with almost 300 species, including the carrion-eating vultures and condors. AH falconiformes have powerful, sharp, hooked beaks for tearing flesh, and strong feet with sharp talons for catching prey. They hunt by day, using their keen eyesight Some, like tne kites, eagles, and buzzards, use soaring or slow-flapping flight to spot their prey on the ground. Others, like the falcons, are fast fliers, catching birds and insects on the wing. Still others have special flying techniques for catching or feeding on fish, snakes, snails, and fruit.

Order Galliformes. Game birds belong to this order. The 10 species of megapodes, which are found exclusively in Australia and Indonesia, are medium-sized, brownish birds known for building huge mounds of soil and vegetation over their eggs. The fermentation of the organic matter in the mounds produces the heat that incubates the eggs. The 18 species of grouse in this order inhabit the temperate and Arctic regions of the Northern Hemisphere. Growing to about the size of a large chicken, they are plump with short bills and legs. There are some 35 species of pheasants, including the red jungle fowl of southern Asia and the East Indies, the peacock, and the smaller partridges and quails. The seven species of guinea fowl live in open country in Africa. The two species of turkeys are found in the woodlands of North America and Central America.

Order Gruiformes. This order includes the ground-nesting, ground-feeding cranes and rails. Many of this order are poor fliers, although the migratory cranes are a striking exception. Large, long-legged, and ranging in color from white to dark gray and brown, the 15 species of cranes have long secondary wing feathers drooping down over the tail. Some have ornamental tufts of feathers on their heads, which are used in their spectacular mating dances. Cranes inhabit marshy areas in Europe, Asia, North America, and Australia. The rails are among the most widespread of all land birds, and are found on all continents. They have also colonized remote oceanic islands. Most island rails have become flightless. They range in size from species as small as sparrows to birds as big as ducks. There are about 130 species of rails. They have long, narrow bodies; short wings and tails; and long legs and toes. The rail group includes the aquatic coots and gallinules.

Order Charadriiformes. This order consists of birds typically found on or near seacoasts and fresh water, including waders, gulls, and their relatives. The waders are a huge group of more than 200 species, ranging from the crow-sized oystercatchers and larger curlews to the medium-sized plovers and diminutive stints. Most are long-legged, and many have long bills for probing for food in mud. The skuas are dark-plumaged, gull-like sea birds with webbed feet, and most have elongated central tail feathers. They feed on fish, small mammals, birds and bird eggs. They also chase gulls, terns, and other birds and force them to disgorge food for their own consumption. There are five or six species. The gulls are a wide-ranging group that includes 43 species from the large, great black-backed gull that grows to about 30 inches (75 centimeters) in length to the 10-inch (25-centimeter) little gull. Gulls are typically grayish or brownish when immature and gray-and-white or black-and-white as adults. Most gulls are coastal, but some live inland. Many have been able to expand their range dramatically, because they feed on food thrown away by humans. Terns are slender sea birds with short legs, webbed feet, and long, pointed bills. They occur in white, gray-and-white, black, or black-and-white and are found worldwide. The auks are short-winged black-and-white diving birds of the northern oceans. Although they can fly, they are most at home in the water. Auks are the northern equivalent to the penguins, also nesting in huge colonies. They range in size from the 6-inch (15-centimeter) little auk to the 30-inch (75-centimeter) extinct great auk. The 22 living species include the familiar puffins.

Order Columbiformes. This order contains the pigeons and their relatives, and includes the extinct dodo. There are 300 species of pigeons and doves found throughout the world, except for Antarctica. They live on seeds, fruits, and berries. Whereas most birds drink by drawing water into the mouth and lifting the head back to swallow, these birds can suck in water without lifting their heads.

Order Psittaciformes. This order consists of approximately 315 species of parrots, which live primarily in the tropics. Varying in size from 3 inches (8 centimeters) to more than 3 feet (91 centimeters) long, most parrots are mainly green, although some are brilliantly colored, and many have long tails and stout, short, strongly hooked bills adapted for feeding on fruits, berries, and seeds.

Order Cuculiformes. This order includes the 19 species of brightly colored touracos from the jungles of Africa and the cuckoos. Some of the cuckoos are parasitic breeders, laying their eggs in the nests of other birds and allowing them to rear their young. More than 100 species of cuckoos are found worldwide. Order Strigiformes. This order is made up of the owls. Most owls are nocturnal birds of prey, with large eyes at the front of their heads; hooked, flesh-tearing bills; razor-sharp talons; and dense, soft plumage, which helps make them almost noiseless at night. They are subdivided into the 10 species of barn owls and bay owls and the 121 species of typical owls. Owls are found throughout the world, except for Antarctica.

Order Caprimulgiformes. This order contains about 95 species of nightjars, sometimes called goatsuckers, and their relatives. They are found worldwide except for Antarctica. These nocturnal birds are related to owls, and they have long, pointed wings and bills ringed with bristles fortrapping flying insects.

Order Apodiformes. All the members of this order, which includes the swifts and hummingbirds, are exceptional fliers with pointed, slender, but powerful wings and tiny feet that are useless for walking. The swifts are the most aerial of all birds, able to sustain flight for many hours. There are about 75 species of swifts and they are found virtually throughout the world. All of the more than 300 known species of hummingbirds live in the Western Hemisphere. Beating their wings as fast as 70 times per second, hummingbirds can hover and even fly backwards. Most are tiny and the largest is only the size of a sparrow. They feed on nectar and insects.

Order Coliiformes. This order consists of the single family of coly, or mousebirds. All six species are African and are small birds with very long, stiff tails and prominent crests.

Order Trogoniformes. This order contains the brightly colored, tree-dwelling, tropical trogons, which have unusually delicate skins. Dark, metallic-blue, -green, or -violet feathers cover the head and back of most males. Their underparts are red, orange, or yellow. The females are duller in color.

Order Coraciiformes. The brightly colored, mainly tropical birds of this order nest in holes in banks or trees, and their front three toes are partly joined. They include the 87 species of kingfishers, 8 species of motmots, approximately 25 species of bee-eaters, 16 species of rollers, 8 species of wood hoopoes and hoopoes, and 44 species of huge-billed hornbills.

Order Piciformes. Birds in this order have feet with two toes pointing forward and two backward. They include the approximately 200 species of woodpeckers, which are specialized for feeding and nesting in tree trunks, and about 40 species of fruit-eating toucans of the tropica! rain forests of Central America and South America.

Order Passeriformes. This order, the perching birds, is the biggest group of all, containing more than a third of all living families and more than half the living species. All have feet adapted to perching on or clinging to branches or other supports. The order includes the “song birds,” which have developed the ability to sing. It also contains the swallows, wagtails, pipits, wrens, thrushes, warblers, tits, finches, weavers, sparrows, starlings, and crows.