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A '''Bird''' is a warm-blooded [[egg]]-laying [[vertebrate]] with [[wing]]s and [[feather]]s.  For the most part, they fly.

'''Bird''' refers to over 10,000 living species of warm-blooded [[vertebrate]] animals of the class Aves, distinguished from all other living animals by the presence of [[feather]]s as an insulating cover, and in the vast majority of species, the ability for powered flight.

[[Ostrich]]es, [[penguin]]s, and [[emu]]s are birds that don't fly, although penguins have sometimes been said to "fly" underwater. [[Robin]]s, [[sparrow]]s, [[cardinal (bird)|cardinal]]s, and [[eagle]]s are more typical flying birds.

Birds are found world-wide on all continents.  Extremely conspicuous, boldly-marked or colored, and readily observable, birds play an important role in nature and in human life. They are environmental monitors, with their rise or decline tied to conditions within their habitats.  Many species are important economically, with poultry farming producing meat, eggs and feathers for human consumption, guano for fertilizer, or bird-watching tourism.  Many, such as canaries and [[parrot]]s, are also kept as pets. Due to human activity, many birds have been domesticated and bred, some have become synanthropic, but at the same time, about 1,200 species are at varying degrees at risk of extinction and are protected by national and international laws.

All birds have two legs and two wings (although in some flightless species such as the [[kiwi]], the wings are very small and serve little purpose). Birds also have a beak, although its shape, size and use varies enormously between species. Uniquely among vertebrates, birds have hollow [[bone]]s; this makes them very light for their size, facilitating flight. Living birds do not have teeth, although some extinct species had teeth. Birds' feathers can be any color, and the colors and pattern often vary between males and females of the same species, with males typically having the more garish and elaborate plumage; in some species such as [[peacock]]s and [[birds of paradise]] this is taken to striking extremes.

 

The smallest bird - and arguably one of the smallest terrestrial vertebrates alive - is the [[bee hummingbird]] (''Mellisuga helenae''), about 2.4 inches long and weighs 0.092 ounces.  The largest was an extinct species of [[elephant bird]] (''Vorombe titan'') of Madagascar, which stood 9.8 feet tall and weighed nearly a ton.  Currently, the largest living bird is the [[ostrich]] (''Struthio camelus''), standing up to 9 feet tall, and weighing up to 320 pounds.

 

All the birds, except the [[moa]]s and elephant birds, have the two front limbs modified in wings and this characteristic allows almost all the species to fly; the feathers on the trailing edges of the wings and tail lengthened, widened, and stiff, enabling birds to not just engage in flight but to be masters at it. Birds' feathers can be any color, and the colors and pattern often vary between males and females of the same species, with males typically having the more garish and elaborate plumage; in many species such as [[peacock]]s and [[birds of paradise]] this is taken to striking extremes.

 

Most birds are highly intelligent, and species such as crows and parrots are considered to be among the most intelligent of animals. Many birds are in fact able to modify and use small objects to pursue their own purposes, and it is now established that in some species there is a transmission of knowledge between generations. They are sociable animals that often live in colonies, communicating thanks to visual or auditory signals. They often participate in social behaviors such as hunting and defense.

== Birds as dinosaurs ==

== Birds as dinosaurs ==