Birds are warm-blooded (endothermic) vertebrate animals that are covered in feathers, lay eggs, typically in a nest and incubated by parents who provide an extended period of care after hatching. All birds have wings, most can fly, some migrate long distances each year, and some cannot fly at all such as ratites and penguins.
There are approximately 10,000 species of birds which range in size from the smallest 5 cm (2 in) bee hummingbird to the largest 2.7 m (8 ft 10 in) ostrich. Birds communicate using visual signals and through calls and songs. They often cooperate together for flocking and sometimes hunting behaviors.
Infectious diseases and man-made influences such as habitat encroachment, pollution, climate disruption have cause many species to become threatened or endangered.