Bird, the only animal with feathers. All birds have feathers and most birds can fly. It is the possession of feathers, not the ability to fly, that distinguishes birds from other animals—some birds are flightless (such as the penguin, ostrich, emu, rhea, and kiwi) and some animals other than birds can fly (insects and bats).Birds vary in size and color, but they all have feathers and wings.
There are about 9,000 known species of birds alive today, of which 700 species live in the United States and Canada. They range in size from the ostrich, which may reach a height of nearly eight feet (2.4 m) and a weight of more than 300 pounds (136 kg), to certain tropical hummingbirds, one of which is only two inches (5 cm) long and weighs less than one ounce (28 g). Birds are found on the icefields of the Arctic and Antarctic, in steaming rain forests and dry desert plateaus, on mountains, in meadows and forests, in crowded cities, and over desolate ocean waters great distances from land. Few spots on earth have not known birds.
The longest-living birds are generally large birds such as ostriches, vultures, eagles, and ravens. These birds live for many decades. Birds also live longer in captivity than in the wild.