In total there are about 11,000 species of birds described as of 2024,[1] though one estimate of the real number places it at almost 20,000.
Taxonomy is very fluid in the age of DNA analysis, so comments are made where appropriate, and all numbers are approximate.
Cladogram of modern bird relationships based on Stiller et al (2024).,[3] showing the 44 orders recognised by the IOC.
[4] Struthioniformes (ostriches) Tinamiformes (tinamous) Rheiformes (rheas) Apterygiformes (kiwis) Casuariiformes (emu and cassowaries) Galliformes (chickens, pheasants, and relatives) Anseriformes (ducks, geese, and relatives) Phoenicopteriformes (flamingos) Podicipediformes (grebes) Columbiformes (pigeons and doves) Mesitornithiformes (mesites) Pterocliformes (sandgrouse) Musophagiformes (turacos) Otidiformes (bustards) Cuculiformes (cuckoos) Opisthocomiformes (hoatzin) Gruiformes (rails and cranes) Charadriiformes (waders, gulls, and relatives) Caprimulgiformes (nightjars) Nyctibiiformes (potoos) Steatornithiformes (oilbirds) Podargiformes (frogmouths) Aegotheliformes (owlet-nightjars) Apodiformes (swifts, treeswifts and hummingbirds) Phaethontiformes (tropicbirds) Eurypygiformes (sunbittern and kagu) Gaviiformes (loons/divers) Procellariiformes (albatrosses, shearwaters, and petrels) Sphenisciformes (penguins) Ciconiiformes (storks) Suliformes (frigatebirds, gannets, cormorants, and darters) Pelecaniformes (pelicans, herons and ibises) Strigiformes (owls) Accipitriformes (hawks, eagles, vultures, and relatives) Coliiformes (mousebirds) Leptosomiformes (cuckoo roller) Trogoniformes (trogons) Bucerotiformes (hornbills, hoopoes and relatives) Coraciiformes (kingfishers, rollers, bee-eaters and relatives) Piciformes (woodpeckers and relatives) Cariamiformes (seriemas) Falconiformes (falcons and caracaras) Psittaciformes (parrots) Passeriformes (passerines) The Palaeognathae or "old jaws" is one of the two superorders recognized within the taxonomic class Aves and consist of the ratites and tinamous.
The ratites are mostly large and long-legged, flightless birds, lacking a keeled sternum.