All birds have feathers, bills, and wings and lay eggs. A hen lays eggs in a nest which takes 21 days to hatch. The chick is wet when it hatches but grows feathers and can walk right away. Chicks resemble their parents and are fully grown into chickens after six months, when female chicks become hens and male chicks become roosters. Scientists disagree on whether birds evolved from small predatory dinosaurs or an earlier reptile.

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

2. • 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!

3. • 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.

4. • 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.

5. • 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.

6. • 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.

7. • 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.