Different types of birds and its characteristics.

Birds compose a diverse class (Aves) of species, as dissimilar as tiny darting hummingbirds and 8-foot flightless ostriches, with about 9,000 living species known. Generally accepted to have evolved from reptilian dinosaurs, birds share several characteristics with other classes of animals, including a skeletal backbone housing a spinal cord, a four-chambered heart and warmbloodedness. Other of birds' characteristics are unique or essentially unique. Feathers : Feathers are the defining characteristic of Aves, found on every living species of bird and no other class of animal. Feathers are made of keratin, the same substance that forms hair and nails in other animals and are highly modified scales. Feathers are critical not only for flight but also for warmth and protection against the elements -- and in many species, for males to attract mates. Soft, fluffy downy feathers help keep birds warm, contour feathers streamline birds’ bodies and aid in flying, and flight ...