Birds have light feathers, which can be either dull or brightly colored and which can keep them warm. Birds keep a constant body temperature so they are considered warm-blooded animals. They have two legs with scaly, clawed feet. Birds have beaks without teeth. While all birds have wings, some do not use them to fly. Ostriches don’t fly, instead, they run at speeds of up to 45 miles per hour! Penguins also do not fly but are excellent swimmers. Birds hatch from eggs with strong shells.