1. Birds

2. • There are over 8,000 species of birds. Birds
have 3 major differentiating characteristics:
wings for flight, feathers, and a beak rather
than teeth.
• Birds have adapted their vertebrate skeleton
for flight. Their bones and skull are very thin,
making their bodies extremely light.
• To support flight also required other changes
to their skeleton. Obvious changes are the
addition of wings.

3. • Other changes are less obvious. The claws and
muscles of a bird's foot are designed to lock and
hold onto a perch even while the bird is sleeping.
• A bird's respiratory system is also adapted to make
it easier to breathe at high elevations, where air is
thinner.