Portal:Birds/Intro
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| A Striated Pardalote (Pardalotus striatus) collecting nesting material in its beak. |
Birds (class Aves) are bipedal, warm-blooded, oviparous vertebrate animals. The earliest known bird is the Jurassic Archaeopteryx. Most scientists believe that birds evolved from theropod dinosaurs. Ranging in size from tiny hummingbirds to the huge Ostrich and Emu, there are between 9,000 and 10,000 known living bird species in the world, making Aves the most diverse class of terrestrial vertebrate. About 120 to 130 human-caused bird extinctions have occurred since 1600; hundreds more have occurred prior.
A bird is characterized by feathers, a beak with no teeth, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a light but strong skeleton. Most birds have forelimbs modified as wings and can fly, although the ratites are flightless, and several other birds, particularly endemic island species, have also lost the ability to fly.
Many species of bird undertake long distance annual migrations, and many more perform shorter more irregular movements. Birds are social animals and communicate using visual signals and through calls and bird song. Birds participate in social behaviours including cooperative hunting, breeding, and flocking. The breeding behaviour of birds is dominated by monogamy, although infidelity is common in some species and other species have polygamous or polyandrous breeding systems. Eggs are usually laid in a nest and incubated. Most birds have an extended period of parental care after hatching.
Humans make use of birds in a number of ways. Birds are important sources of food, acquired either through farming or hunting. Numerous species of birds are also used commercially, and some species, particularly songbirds and parrots, are popular pets. Birds figure prominently in all aspects of human culture from religion to poetry and popular music. Numerous species of birds are threatened with extinction by human activities and efforts are underway to protect them.