A bird is the only animal that has feathers. Also, all birds have bills, have wings, and lay eggs.

• Eggs: A hen lays eggs in a nest. Some eggs have an embryo inside. An embryo will grow into a chick in 21 days. The mother hen must keep the egg warm. The egg's hard shell protects it while it grows. The baby bird will use an egg tooth on it's beak to hatch out of the egg. This can take a full day!

• Chick: The chick is wet when it hatches from its egg. It has feathers called down. The down will dry fast. Also, chicks can walk right away. They like to eat seeds, bugs, and worms. Chicks grow more feathers in about 4 weeks. A comb grows on the chick's head and a wattle grows under the chick's beak. Chicks resemble their parents from the time they hatch and as they grow.

• Chicken:  Chicks are fully grown into chickens in six months. Female chicks grow up to be hens. Male chicks grow up to be roosters. The hens will lay more eggs.

• Scientists disagree about many aspects of the evolution of birds. Many paleontologists (scientists who study fossils to learn about prehistoric life) believe that birds evolved from small, predatory dinosaurs called theropods.

• These scientists say that many skeletal features of birds, such as light, hollow bones and a furculum, were present in theropod dinosaurs prior to the evolution of birds.

• Others, however, think that birds evolved from an earlier type of reptile called thecodonts—a group that ultimately gave rise to dinosaurs, crocodiles, and the flying reptiles known as pterosaurs.

• These scientists assert that similarities between birds and theropod dinosaurs are due to a phenomenon called convergent evolution—the evolution of similar traits among groups of organisms that are not necessarily related.