What is a Bird?
Birds are in the biological classification Aves. They are winged, bipedal vertebrate animals that lay eggs. There are about 10,000 species of birds throughout the world that range in size from about 2 inches for the smallest hummingbird to the ostrich at over 8 feet tall.
Birds evolved from dinosaurs during the Jurassic period, and modern birds are characterized by feathered bodies, a light-weight strong skeleton, a beak with no teeth, a four-chambered heart, and the laying of eggs with hard shells. Birds also have unique digestive and respiratory systems that are adapted for flight. Many species of birds are highly intelligent, such as the corvids and parrots.
Migration is the regular seasonal journey that many birds undertake. Most birds are social species and communicate through visual displays, songs, and calls. Most birds are monogamous, choosing one mate per breeding season. Eggs are usually laid in a nest and cared for by both parents.
Currently, about 1,200 species of birds are in danger of extinction due to human activity.