What Is a Bird?

There are about 10,000 bird species, found in every shape and size, from the tiny hummingbird to the majestic condor. They occur in all the colors of the rainbow and are loved for their musical songs. Some birds can even mimic human speech. All birds lay eggs to incubate their young, and all have feathers—a trait no other animals can claim. Birds also have wings, evolutionary adaptations of ancient forelimbs. Most use their wings for flight, but others, like ostriches and penguins, are grounded.