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In nature, birds of the same species in flight often form homogeneous groups for various reasons, such as to defend against predators. This behavior of birds has been observed by people since time immemorial, and is the source of the idiom ("of a feather" means "of the same plumage," that is, of the same species).
The flight of some species is characterised by a distinctive "flicking" action quite different from swallows. Swifts range in size from the pygmy swiftlet ( Collocalia troglodytes ), which weighs 5.4 g and measures 9 cm (3.5 in) long, to the purple needletail ( Hirundapus celebensis ), which weighs 184 g (6.5 oz) and measures 25 cm (9.8 in) long.
However, the claw curvature of the hand in Archaeopteryx was similar to that in basal birds. Based upon the comparisons of modern birds to Archaeopteryx, perching characteristics were present, signifying an arboreal habitat. The ability for takeoff and flight was originally thought to require a supracoracoideus pulley system (SC).
Birds (flying, soaring) – Most of the approximately 10,000 living species can fly (flightless birds are the exception). Bird flight is one of the most studied forms of aerial locomotion in animals. See List of soaring birds for birds that can soar as well as fly. Townsends's big-eared bat, (Corynorhinus townsendii) displaying the "hand wing"
Bird flight is the primary mode of locomotion used by most bird species in which birds take off and fly. Flight assists birds with feeding, breeding , avoiding predators , and migrating . Bird flight includes multiple types of motion, including hovering, taking off, and landing, involving many complex movements.
A kettle is a group of birds wheeling and circling in the air. The kettle may be composed of several different species at the same time. Nature photographer M. Timothy O'Keefe theorizes that the word derives from the appearance of birds circling tightly in a thermal updraft "like something boiling in a cauldron."
The steppe birds are more popular to hunt because they can be flushed into flight, rather than the forest birds that run to cover and hide. In the late 19th and early 20th century hunting was responsible for mass killing within the family, with the elegant crested tinamou and spotted nothura popular targets.
Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which are modified forelimbs , gave birds the ability to fly, although further evolution has led to the loss of flight in some birds , including ratites , penguins , and diverse endemic island species.