The class Aves is the birds. Birds are vertebrates with feathers, modified for flight and active metabolism. There are a few kinds of birds that don't fly. Modern birds have the following traits:
• horny beak, no teeth
• large muscular stomach
• large yolked, hard-shelled eggs.
• strong skeleton Birds provides extensive care of their young until it is grown, or gets some other bird to look after the young. The birds are divided in to 30 orders.