the most notable characteristics of birds are their ability to sing and their variety. we sometimes wonder how birds fly. this is possible because the bones of a bird are hollow. this makes them light. they also have strong muscle across the chest. birds wings are usually very strong. their singing ability also sets them apart from other animals. sometimes their singing is high ad shrill; other times it is low and raucous. finally, there is the variety of types of birds. there are water birds,such as ducks and swans. there are birds of prey, such as haws and eagles. there are birds that do not fly, like the ostrich.birds are quite varied.