The shell of the egg is hard and brittle. The color of the egg helps to hide it from predators. The egg tooth, which is on the end of the baby bird's beak, falls off after the baby bird has gotten out of the egg shell. Since baby birds are born with no feathers, the parents must feed them until they learn to fly and get food on their own. Birds are warm-blooded which means that their body temperature remains constant even when the temperature of their environment changes.
All birds have two legs with four toes each.
Three of the toes face forward and one of the toes faces backwards. Birds use their toes to wrap around a wire or tree branch so that they can perch without falling. Birds also have two wings. The wings are covered in feathers. Birds, like mammals, have lungs.