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Scientific name: Aves


Birds - Aves

Birds - Aves

Photo courtesy Shutterstock.
Hummingbirds and swifts - Apodiformes

Hummingbirds and swifts - Apodiformes

Photo © Ed Reschke / Getty Images.
Photo © Iwan Tirtha / Getty Images.

Birds (Aves) are a group of vertebrates that have wings, feathers, hollow bones and numerous other adaptations for an aerial lifestyle. Birds are classified into about 30 groups, some of which include albatrosses, gamebirds, herons, hummingbirds, kingfishers, loons, owls, parrots, penguins, perching birds, pigeons, waterfowl, woodpeckers and many others. There are between 9,000 and 10,000 species of birds alive today. Birds evolved from reptiles during the Mesazoic Era about 150 million years ago.

Birds possess distinct characteristics that make them one of the most distinguishable group of vertebrates. Feathers provide insulation and enable flight (feathers are modifications of a bird's epidermis). Birds do not possess teeth or the heavy jawbones seen in other vertebrates. Instead, birds have a pair of toothless mandibles that are covered with a horny sheath of keratin (this sheath that covers the mandible is also called the ramphotheca). Birds have a furcula, a bone that is also known as the 'wishbone'. The furcula is a bone located in the bird's chest that prevents compression of the chest cavity during the downstroke of a wingbeat.

Key Characteristics

The key characteristics of birds include:

  • feathers
  • bills
  • furcula
  • fused bones in pelvis, feet, hands, and head
  • lightweight bones (bones that are either hollow or spongy/strutted)
  • no teeth or maxillary bones of the jaw (reduces anterior weight)
  • endothermic
  • four-chambered heart and exhibit high metabolic rates
  • produce large, richly provisioned external eggs
  • remarkable navigational abilities in many species
  • extraordinary communication and song production


Birds are classified within the following taxonomic hierarchy:

Animals > Chordates > Vertebrates > Tetrapods > Birds

Birds are divided into the following taxonomic groups:

  • Albatrosses and petrels (Procellariiformes) - There are about 107 species of albatrosses and petrels alive today. Members of this include albatrosses, fulmars, prions, shearwaters, storm-petrels and diving petrels. Albatrosses and petrels are pelagic birds that spend prolonged periods of time flying and foraging at sea.
  • Birds of prey (Falconiformes) - There are about 304 species of birds of prey alive today. Members of this group include falcons, accipiters, osprey and the secretary bird. Birds of prey are formidable avian predators, armed with powerful talons, hooked beaks and acute eyesight.
  • Buttonquail (Turniciformes) - The buttonquail form a small group of birds consisting of 15 species. Members of this group incluce the quail plover, painted buttonquail, sumba buttonquail, and about a dozen other species. Buttonquail are ground-dwelling birds that inhabit the warm grasslands, scrublands and croplands of Europe, Asia, Africa and Australia.
  • Cassowaries and emus (Cassowariiformes) - There are three species of cassowaries and one species of emu. Members of this group include the southern cassowary, dwarf cassowary, northern cassowary, and emu. Cassowaries and emus are large flightless birds that have a long neck and long legs.
  • Cranes, coots, and rails (Gruiformes) - There are about 199 species of cranes, coots, and rails alive today. Members of this group inclue coots, rails, crakes, bustards, and trumpeters. Cranes, coots, and rails are varied in their size and appearance, but generally have a short tail, long neck and rounded wings.
  • Cuckoos and turacos (Cuculiformes) - There are about 161 species of cuckoos and turacos alive today. Members of this group generally have a bulky body, small head, short beak long tail and broad wings. Cuckoos are dull colored birds but turacos have brighter with vibrant reds and green plummage.
  • Flamingos (Phoenicopteriformes) - There are five species of flamingos alive today. Members of this group include the greater flamingo, lesser flamingo, Chilean flamingo, James's flamingo Andean flamingo and American flamingo. Flamingos are filter-feeding birds that survive on a diet of brine shrimp and blue-green algae.
  • Gamebirds (Galliformes) - There are about 250 species of gamebirds alive today. Members of this group include chickens, pheasants, turkeys, quails, grouse, currasows, guans, chachalacas, guineafowl and megapodes. Gamebirds are excellent runners and can fly short distances.
  • Grebes (Podicipediformes) - There are about 21 species of grebes alive today. Members of this group include little grebes, pied-billed grebes, Titicaca grebes, red-necked grebes, western grebes and many others. Grebes are medium-sized freshwater diving birds that have worldwide distribution.
  • Herons, storks, and relatives (Ciconiiformes) - There are about 115 species of herons, storks and their relatives alive today. Members of this group include herons, storks, ibises, spoonbils sandpipers, petrels, and shearwaters. Herons, storks and their relatives are long-legged, sharp-billed carnivorous birds that inhabit freshwater wetlands.
  • Hummingbirds and swifts (Apodiformes) - There are about 429 species of hummingbirds and swifts alive today. Members of this group have long, narrow wings and dainty legs and feet. Hummingbirds feed on nectar and swifts are aerial hunters that feed on insects.
  • Kingfishers (Coraciiformes) - There are about 208 species of kingfishers alive today. Members of this group include kingfishers, bee-eaters, rollers, hornbills, and hoopies. Kingfishers have a large head, powerful bills, and a unique pattern of feather tracts.
  • Kiwis (Apterygiformes) - There are three species of kiwis alive today. Members of this group are small, flightless, nocturnal birds endemic to New Zealand. Kiwis forage at night on the forest floor. They probe their bills into the loose debris and vegetation in search of earthworms.
  • Loons (Gaviiformes) - There are five species of loons alive today. Loons are a group of freshwater diving birds that inhabit northern lakes throughout North America and Eurasia. Loons have the smallest wing-to-weight ration of all birds but this does not mean they are unskilled fliers.
  • Mousebirds (Coliiformes) - There are six species of mousebirds alive today. Mousebirds are a small group of birds that inhabit open woodlands, scrublands and savannas in sub-Saharan Africa. They have a distinct crest and strong legs.
  • Nightjars and Frogmouths (Caprimulgiformes) - There are about 115 species of nightjars and frogmouths alive today. Members of this group are nocturnal birds that feed on insects that they catch in flight or by foraging on the ground. Nightjars and frogmouths are brown, black, buff and white in color and their feather pattern is often quite mottled.
  • Ostrich and rheas (Struthioniformes) - There one species of ostrich and two species of rheas alive today. The ostrich is the tallest and the heaviest species of all living birds. Rheas, like ostriches, have flat breastbones that lack a keel, the bone structure to which flight muscles attached. They have long, shaggy feathers and three toes on each foot. Ostriches and rheas are flightless birds that have adapted to life on the ground with impressive agility. 
  • Owls (Strigiformes) - There are 194 species of owls alive today. Members of this group include true owls and barn owls. Owls are nocturnal hunters that locate their prey using a combination of sight and sound. Their eyes are large, enabling them to gather ample light under dim conditions.
  • Parrots (Psittaciformes) - There are about 352 species of parrots alive today. Members of this group include lorikeets, cockatiels, parakeets, budgerigars, macaws, and broad-tailed parrots. Parrots are colorful, social birds that form large noisy flocks.
  • Pelicans and relatives (Pelicaniformes) - There are about 64 species of pelicans and their relatives alive today. Members of this group include pelicans, gannets, boobies, cormorants, anhingas, tropicbirds and frigatebirds. Pelicans and their relatives are an ancient clan of birds with a fossil record that stretches back 100 million years.
  • Penguins (Sphenisciformes) - There are 18 species of penguins alive today. Members of this group include crested penguins, banded penguins, little penguins, brush-tailed penguins, great penguins and megadyptes. Penguins are flightless birds that have stiff wings and distinct black and white coloration.
  • Perching birds (Passeriformes) - There are more than 5,200 species of perching birds alive today. Members of this group include tits, sparrows, finches, wrens, dippers, thrushes, starlings, warblers, crows, jays, wagtails, swallows, larks, martins, warblers and many others. Perching birds have a unique foot structure that enables them to grip onto thin branches, twigs, slender reeds and flimsy grass stems.
  • Pigeons and doves (Columbiformes) There are 312 species of pigeons and doves alive today. Members of this group include Old World pigeons, American pigeons, bronzewings, quail-doves, American ground doves, Indopacific ground doves, crowned pigeons and many other groups. Pigeons and doves are small to medium sized birds and have short legs, a portly body, short neck and small head.
  • Sandgrouse (Pteroclidiformes) - There are 16 species of sandgrouse alive today. Members of this group include the pin-tailed sandgrouse, black-faced sandgrouse, yellow-throated sandgrouse, and many others.
  • Shorebirds (Charadriiformes) - There are 344 species of shorebirds alive today. Members of this group include waders, auks and gulls. Shore birds live in coastal areas including shorelines and beaches. Many species probe the soft sand and sediment to feed on insects, worms and other small aquatic animals.
  • Tinamous (Tinamiformes) - There are 47 species of tinamous alive today. Members of this group include the highland tinamou, red-winged tinamou, dwarf tinamou, Andean tinamou, and many other species. Tinamous live in North and South America, southern Asia and sub-Saharan Africa.
  • Trogons (Trogoniformes) - There are 39 species of trogons alive today. Members of this group include the eared quetzal, blue-crowned trogon, scarlet dumped trogon, Javan trogon and many other species.
  • Waterfowl (Anseriformes) - There are 157 species of waterfowl alive today. Members of this group include swans, ducks, geese, and screamers. Waterfowl are well adapted for life in aquatic habitats.
  • Woodpeckers (Piciformes) - There are 396 species of woodpeckers alive today. Members of this group include toucans, puffbirds, jacamars, barbets and honeyguides. Woodpeckers feed on fruit and insects. One group in particular, the honeyguides, live on a diet of beeswax.


Gill F. Ornithology. New York NY: WH Freeman and Company; 1990. 660 p.

Burger J. Birds: A Visual Guide. Richmond Hill, Ontario: Firefly Books; 2006. 303 p.

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