Birds

Birds are a group of warm-blooded theropod dinosaurs constituting the class Aves, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the bee hummingbird to the common ostrich. There are over 11,000 living species and they are split into 44 orders. More than half are passerine or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds.

seasonal movement of birds

thumb|The distance A to B is the wingspan of this Boeing 777-200ER

group of birds conducting flocking behavior in the midst of flight, or while foraging or roosting

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long, stiff feather on the wing or tail of a bird that aids in the generation of lift and thrust

thumb|Two children with parrot cage (painting by Georg Friedrich Kersting, c. 1835) thumb|British birdcage, c. 1750, mahogany and brass, overall: Metropolitan Museum of Art (New York City)

grouping of eggs in a nest

birds that are poisonous to touch and eat

swarming behaviour of birds when foraging

thumb|The Rooks Have Returned|The Rooks Have Come Back Again, [[Alexei Savrasov, 1871, canvas, oil, The Tretyakov Gallery, Moscow]] thumb|Colonies of Indian yellow-nosed albatross|Indian yellow-nosed albatrosses on [[Amsterdam Island]] thumb|Fur seals in a rookery in the [[Pribilof Islands in the 1950s.]] A rookery is a colony of breeding rooks, and more broadly a colony of several types of breeding animals, generally gregarious birds.

mucous membrane produced by bird nestlings

animal behavior; storage of food in hidden locations

social structure in which juveniles and sexually mature adolescents remain with their parents and help them raise subsequent broods instead of dispersing and reproducing themselves

natural phenomenon

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