What makes a bird birds are vertebrates with feathers they have distinctive bills are endothermic produce large eggs have elaborate parental behavior birds are vertebrates with feathers they have distinctive bills are endothermic produce large eggs have elaborate parental behavior. Feathers all birds have evolved feathers composed of keratin and other proteins and light reflecting pigments to serve as body insulation different types of feathers may also be ornamental such as plumes crests or streamers other feather types help birds control their flight while some feathers such as down are strictly for insulation. Unique bird characteristics what makes a bird a bird birds were able to become flying machines largely through the evolutionary gifts of feathers powerful wings hollow bones warm blood a remarkable respiratory system and a large strong heart. What makes a bird a bird background there are more than 9000 species of birds in the world with about 800 found in north america more than 400 species have been recorded in illinois and more than 200 bird species have been recorded as nesting in the state birds evolved from small reptiles more than 160 million years ago they still share some characteristics with reptiles such as laying