Class Aves: Birds

Birds are bipedal, endothermic (warm-blooded), vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.7 m (9 ft) Ostrich. The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, around 150–200 Ma (million years ago), and the earliest known bird is the Late Jurassic Archaeopteryx, c 155–150 Ma.

Modern birds are characterised by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. All birds have forelimbs modified as wings and most can fly, with some exceptions including ratites, penguins, and a number of diverse endemic island species. Birds also have unique digestive and respiratory systems that are highly adapted for flight. Some birds, especially corvids and parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools, and many social species exhibit cultural transmission of knowledge across generations.

Many species undertake long distance annual migrations, and many more perform shorter irregular movements. Birds are social; they communicate using visual signals and through calls and songs, and participate in social behaviours including cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of bird species are socially monogamous, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are polygynous ("many females") or, rarely, polyandrous ("many males"). Eggs are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching.

Many species are of economic importance, mostly as sources of food acquired through hunting or farming. Some species, particularly songbirds and parrots, are popular as pets. Other uses include the harvesting of guano (droppings) for use as a fertiliser. Birds figure prominently in all aspects of human culture from religion to poetry to popular music. About 120–130 species have become extinct as a result of human activity since the 17th century, and hundreds more before then. Currently about 1,200 species of birds are threatened with extinction by human activities, though efforts are underway to protect them.

SuperOrder Paleognathae

The flightless and mostly giant Struthioniformes lack a keeled sternum and are collectively known as ratites. Together with the Tinamiformes, they form the Paleognathae (or 'old jaws'), one of the two evolutionary "super orders".

Order Struthioniformes: mainly southern hemisphere; 12 species, 5 vulnerable, 2 extinct since 1600
- Family Struthionidae: Ostrich
- Family Casuariidae: emus and cassowaries
- Family Apterygidae: kiwis
- Family Rheidae: rheas
Order Tinamiformes: South America; 45 species, 5 vulnerable, 2 endangered, 2 possibly extinct since 1600
- Family Tinamidae: tinamous

Super Order Neognathae

Nearly all living birds belong to the super order of Neognathae— or 'new jaws'. With their keels, unlike the ratites, they are known as carinates. The passerines alone account for well over 5000 species.

Order Anseriformes: worldwide; ~150 species

Family Anhimidae: screamers
Family Anseranatidae: Magpie-goose
Family Anatidae: swans, geese and ducks

Order Galliformes: worldwide except northern Eurasia; ~250 species

Family Megapodidae: mound-builders
Family Cracidae: chachalacas, guans and curassows
Family Tetraonidae: grouse
Family Phasianidae: partridges, pheasants, quail and allies
Family Odontophoridae: New World quails
Family Numididae: guineafowl
Family Meleagrididae: turkeys
Family Mesitornithidae: mesites

Order Sphenisciformes: Antarctic and southern waters; 17 species, 7 vulnerable, 3 endangered
- Family Spheniscidae: penguins
Order Gaviiformes: North America, Eurasia; 5 species
- Family Gaviidae: loons or divers
Order Procellariiformes: pan-oceanic; 120 species
- Family Diomedeidae: albatrosses ;14 species, 8 vulnerable, 1 endangered
- Family Procellariidae: fulmars, prions, shearwaters, gadfly and other petrels ; 72 species, 20 vulnerable, 11 endangered
- Family Pelecanoididae: diving petrels ; 4 species, 1 endangered
- Family Hydrobatidae: storm petrels ; 20species, 1 vulnerable
Order Pelecaniformes: worldwide; 66 species
- Family Pelecanidae: pelicans ; 8 species, 1 vulnerable
- Family Sulidae: gannets and boobies ; 9 species, 1 vulnerable, 1 endangered
- Family Phalacrocoracidae: cormorants ; 39 species, 8 vulnerable, 2 endangered and 1 extinct since 1600
- Family Fregatidae: frigatebirds ; 5 species, 1 vulnerable, 1 endangered
- Family Anhingidae: Anhinga and darters ; 2 species
- Family Phaethontidae: tropicbirds ; 3 species
Order Ciconiiformes: all continents; More than 100 species.
- Family Ardeidae: herons and bitterns
- Family Balaenicipitidae: Shoebill
- Family Scopidae: Hammerkop
- Family Ciconiidae: storks
- Family Threskiornithidae: ibises and spoonbills
Order Phoenicopteriformes: worldwide; 6 species, 1 vulnerable
- Family Phoenicopteridae: flamingoes
Order Podicipediformes: worldwide; 19 species, 2 vulnerable, 1 endangered, 2 or 3 extinct since 1600
- Family Podicipedidae: grebes
- Family Cathartidae: New World vultures and Condors, - sometimes placed in Falconiformes/Accipitriformes.
Order Falconiformes worldwide; ~260 species. Sometimes all except the falcons are separated as Accipitriformes.
- Family Pandionidae: Osprey
- Family Accipitridae: hawks, eagles, buzzards and Old World vultures, harriers, kites, and allies
- Family Sagittaridae: Secretary Bird
- Family Falconidae: falcons
Order Gruiformes: worldwide; ~200 species
- Family Gruidae: cranes
- Family Aramidae: Limpkin
- Family Psophiidae: trumpeters
- Family Rallidae: rails, crakes, coots and allies
- Family Heliornithidae: finfoots and Sungrebe
- Family Rhynochetidae: Kagu
- Family Eurypygidae: Sunbittern
- Family Cariamidae: seriemas
- Family Otididae: bustards
Order Charadriiformes: worldwide; >300 species
- Family Scolopacidae: typical waders or shorebirds
- Family Rostratulidae: painted snipe
- Family Jacanidae: jacanas
- Family Thinocoridae: seedsnipe
- Family Pedionomidae: Plains Wanderer
- Family Laridae: gulls
- Family Rhynchopidae: skimmers
- Family Sternidae: terns
- Family Alcidae: auks
- Family Stercorariidae: skuas
- Family Glareolidae: coursers and pratincoles
- Family Dromadidae: Crab Plover
- Family Turnicidae: buttonquails
- Family Burhinidae: thick-knees
- Family Chionididae: sheathbills
- Family Pluvianellidae: Magellanic Plover
- Family Ibidorhynchidae: Ibisbill
- Family Recurvirostridae: avocets and stilts
- Family Haematopodidae: oystercatchers
- Family Charadriidae: plovers and lapwings
Order Pterocliformes: Africa, Europe, Asia; 16 species
- Family Pteroclidae: sandgrouse
Order Columbiformes: worldwide; ~300 species
- Family Raphidae: Dodo and Rodriguez Solitaire
- Family Columbidae: pigeons and doves
Order Psittaciformes: pan-tropical, southern temperate zones; ~330 species
- Family Cacatuidae: cockatoos
- Family Psittacidae: parrots
Order Cuculiformes: worldwide; ~150 species
- Family Musophagidae: turacos and allies
- Family Cuculidae: cuckoos
- Family Opisthocomidae: Hoatzin
Order Strigiformes: worldwide; >130 species
- Family Tytonidae: barn owls
- Family Strigidae: true owls
Order Caprimulgiformes: worldwide; ~100 species
- Family Steatornithidae: Oilbird
- Family Podargidae: frogmouths
- Family Nyctibiidae: potoos
- Family Aegothelidae: owlet-nightjars
- Family Caprimulgidae: nightjars
Order Apodiformes: worldwide; >400 species
- Family Apodidae: swifts
- Family Hemiprocnidae: tree swifts
- Family Trochilidae: hummingbirds - sometimes separated as Trochiliformes
Order Coliiformes: Sub-Saharan Africa; 6 species
- Family Coliidae: mousebirds
Order Trogoniformes: Sub-Saharan Africa, Americas, Asia; 35 species
- Family Trogonidae: trogons and quetzals
Order Coraciiformes: worldwide; ~200 species
- Family Alcedinidae: river kingfishers
- Family Halcyonidae: tree kingfishers
- Family Cerylidae: water or belted kingfishers
- Family Todidae: todies
- Family Momotidae: motmots
- Family Meropidae: bee-eaters
- Family Leptosomatidae: Cuckoo Roller
- Family Brachypteraciidae: ground rollers
- Family Coraciidae: rollers
- Family Upupidae: Hoopoe
- Family Phoeniculidae: woodhoopoes
- Family Bucerotidae: hornbills
Order Piciformes: worldwide except Australia; ~400 species
- Family Galbulidae: jacamars
- Family Bucconidae: puffbirds
- Family Capitonidae: barbets
- Family Indicatoridae: honeyguides
- Family Ramphastidae: toucans
- Family Picidae: woodpeckers
Order Passeriformes: worldwide; >5000 species
- Suborder Acanthisitti
- Suborder Tyranni ("suboscines")