The following classification follows the traditional 27-order model, a long-standing morphological model based on careful observations of anatomical similarities between birds. I use this system even though it is quite old, and many scientists are in favor of changing it. Cladistic taxonomists, in particular, have compared DNA between bird groups to make many sweeping changes (including, for example, a radical revision of Order Ciconiiformes, so that it includes penguins, loons, grebes, albatrosses, and birds of prey). This system remains quite controversial, however, and in the absence of any universally recognized classification of birds, I have simply defaulted to the traditional 27-order system.

For writing the descriptions of each group of birds, the most useful source I found was Birds of the World by Oliver L. Austin (1960)—an old book, but a really good one. I also took additional information from Bird Families of the World, edited by C. J. O. Harrison (1978), and a few others.

The bird species figures are from Ornithology, 2nd ed., by Frank B. Gill (1995).

	Described living species					Stories
	Class Aves. Birds. Birds comprise perhaps the most distinctive class of animals, for they all possess feathers, a feature shared by no other animal.				9,620
		Subclass Archaeornithes. An extinct subclass of primitive, reptile-like birds, related to the first birds that evolved from dinosaurs at least 150 million years ago.			—
		Subclass Neornithes. This subclass includes all living birds: ostriches to eagles, penguins to sparrows. It arose during the Cretaceous Period, at least 70 million years ago, and has lived up to the present day.			9,620
			Superorder Palaeognathae. A small group of large, primitive birds, distinguished by the fact that their mouths resemble those of prehistoric reptiles. Included are the large, flightless ratites (ostriches, rheas, emus, cassowaries, and kiwis) and the tinamous.		57
				Order Struthioniformes. The ostrich. The largest living bird, weighing 90 to 130 kg (200 to 285 lbs.) and standing 2 m (6 1/2 ft.) tall. It is flightless, and lives in the drier regions of Africa.	1
				Order Rheiformes. Rheas. Large, flightless, ostrich-like birds of South America.	2
				Order Casuariiformes. Cassowaries and emus. Flightless birds of Australia and New Guinea. Emus are shaped like squat, short ostriches, while cassowaries look a little bit like large turkeys.	4
				Order Apterygiformes. Kiwis. The national birds of New Zealand, kiwis are small, flightless, earthworm-eating birds, with shaggy feathers and long noses.	3
				Order Tinamiformes. Tinamous. A single large family of stout birds of Central and South America. Unlike their larger relatives, the ratites, tinamous are able to fly, although they spend most of their time on the ground.	47
			Superorder Neognathae. Modern birds, including the vast majority that are alive today, possessing a flexible, bird-like mouth.		9,563
				Order Sphenisciformes. Penguins. Of all birds, the distinctive black-and-white penguins are probably the best adapted for swimming, and catch their prey exclusively underwater. They live on Antarctica and throughout the shores of the southern hemisphere.	17	Penguin
				Order Gaviiformes. Loons (American English) or divers (British English). Distinctive birds that gain food by diving for fish, inhabiting freshwater lakes throughout northern North America and Eurasia.	5
				Order Podicipediformes. Grebes. Water birds, rather like loons in their appearance, and in the fact that they dive in lakes for food. They are widely distributed throughout the world.	21
				Order Procellariiformes. Tube-nosed seabirds. These birds, with their distinctive tube-like nostrils, fly over vast regions of the sea as they hunt for fish and invertebrates. Albatrosses, shearwaters, petrels, and fulmars.	115
				Order Pelecaniformes. Pelicans and their allies. A widely varied group of birds, all aquatic, and all with distinctive webs between their four toes. Pelicans, cormorants, boobies, gannets, anhingas (darters), frigatebirds, and tropicbirds.	67
				Order Ciconiiformes. Herons and their allies. Long-legged and often long-necked birds, eating all kinds of food, especially aquatic food. Herons, bitterns, storks, ibises, spoonbills, flamingos, and the hammerhead.	125	Stork
				Order Anseriformes. Waterfowl. The vast majority of this order consists of waterfowl, a familiar, worldwide family of aquatic birds, including ducks, swans, and geese; also included are trumpeters, a smaller family of aquatic birds of South America.	161
				Order Falconiformes. Raptors (birds of prey). Birds of prey are highly recognized and admired, and are characterized by their large, hooked bills, their strong talons, and their carnivorous habits. Examples include eagles, hawks, vultures, falcons, condors, buzzards, kites, harriers, the osprey, the secretary bird, and others.	311
				Order Galliformes. Fowl-like gamebirds and their allies. Many members of this group are well-known around the world as gamebirds and even as domesticated fowl. Included are grouse, quails, partridges, pheasants (including the common chicken), ptarmigan, turkeys, curassows, guans, chachalacas, megapodes, and others.	258
				Order Gruiformes. Cranes, rails, and their allies. A diverse collection of bird families, many living around fresh water or in marshes. A disproportionate number of them are either endangered or recently extinct. Included are cranes, rails, coots, gallinules, bustards, trumpeters, limpkins, finfoots, seriemas, hemipodes, mesites, and others.	213
				Order Charadriiformes. Gulls and their allies. A diverse order of birds, distributed throughout the world, mostly carnivorous, and possessing in common a distinctive oil gland as well as similarities of feather and mouth anatomy. Included are gulls, terns, skuas, jaegers, skimmers, auks, puffins, jaçanas, snipes, oyster catchers, plovers, lapwings, sandpipers, stilts, avocets, phalaropes, sheathbills, and others.	366
				Order Columbiformes. Pigeons and their allies. A successful, widespread group of ground birds with thick, heavy plumage. Included are pigeons, doves, sandgrouse, and (extinct) dodos.	313
				Order Psittaciformes. Parrots. Parrots comprise a very successful and widespread family, and one so unique that it has been given its own order. These mostly herbivorous birds have a highly distinctive appearance, including a stout, curved beak.	358	Budgie
				Order Cuculiformes. Cuckoos and their allies. A collection of long-bodied, long-tailed birds, living around the world. Examples include cuckoos (including the roadrunner), anis, coucals, turacos, and others.	166
				Order Strigiformes. Owls. Though not related to raptors (the so-called "birds of prey"), owls are every bit as successful as they at catching prey. Of all the birds, they alone have adapted to the tough challenge of hunting at night, and are easily recognized by their forward-facing eyes surrounded by facial discs.	178
				Order Caprimulgiformes. Nightjars and their allies. A widespread group of birds with long wings, delicate legs, and a short bill. Included are nightjars (goatsuckers), frogmouths, owlet-nightjars, and others.	113
				Order Apodiformes. Swifts and hummingbirds. Swifts are, of all birds, seemingly the most addicted to flight-eating, drinking, mating, collecting nest material, and even sometimes sleeping on the wing. Hummingbirds are among the most distinctive birds in the New World—small, long-billed, colorful, capable of hovering, and specialized for nectar-eating.	422
				Order Coliiformes. Mousebirds, or colies. A small family of small African birds with distinctive long tails of ten feathers.	6
				Order Trogoniformes. Trogons. A single family of birds with colorful feathers and delicate skin, distributed throughout the world's tropical regions, especially in Latin America.	39
				Order Coraciiformes. Kingfishers and allies. A diverse assemblage of brightly-colored birds, mostly tropical and subtropical (though worldwide), characterized by a distinctive joining of their three front toes. Included are kingfishers, hornbills, bee-eaters, motmots, todies, rollers, hoopoes, and others.	218
				Order Piciformes. Woodpeckers and their allies. Solitary, mostly arboreal (tree-living) birds, distributed throughout the world, having specialized bills, unique thigh muscles, and feet with two toes pointing forwards and two backwards. Woodpeckers, toucans, barbets, puffbirds, honeyguides, and jacamars.	410
				Order Passeriformes. Passerines, or perching birds. This is by far the largest order of birds, containing some 59% of all bird species. Ever since they first evolved some 95 million years ago, passerine birds have proliferated more than any other bird order, so that today they are common and widespread throughout the world. Passerines are characterized by their thin legs with four toes, three in front and one behind. Included in this order are accentors, antbirds, asities, babblers, bell magpies, birds of paradise, blackbirds, bowerbirds, broadbills, bulbuls, buntings, Cardinal grosbeaks, catbirds, chats, cotingas, creepers, crows, cuckoo shrikes, dippers, drongos, fairy wrens, figbirds, finches, flowerpeckers, flycatchers, gnateaters, helmet shrikes, honeycreepers, honeyeaters, icterids, jays, larks, leafbirds, linnets, logrunners, lyrebirds, magpie larks, magpies, manakins, martins, minivets, mockingbirds, mudnesters, New Zealand wrens, nuthatches, orioles, ovenbirds, pardalotes, parrotbills, pepper shrikes, pipits, pittas, plantcutters, scrub birds, seedeaters, shrikes, sparrows, spiderhunters, starlings, sunbirds, swallows, tanagers, tapaculos, thickheads, thrashers, thrushes, titmice, tits, treecreepers, tyrant flycatchers, vanga shrikes, vireos, wagtails, warblers, wattlebirds, waxbills, waxwings, weavers, white-eyes, woodcreepers, wood swallows, wood warblers, wrens, and many others.	5,681	Raven

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