Chapter 18: Vertebrate Animals

Figure 13 Wings provide an upward force called lift in
both birds and airplanes.
Bald eagles are able to soar for long periods of time
because their wings have a large surface area to
provide lift.
The glider gets lift from its wings the same way a bald
eagle gets lift.
Topic: Wing Designs
Visit red.msscience.com for Web
links to information about wing
designs of different aircraft.
Activity Draw as many wing
designs as you can find and explain
how they are different.
Adaptations for Flight
The bodies of most birds are designed for flight. They are
streamlined and have light yet strong skeletons. The inside of a
bird’s bone is almost hollow. Internal crisscrossing structures
strengthen the bones without making them as heavy as mammal
bones are. Because flying requires a rigid body, a bird’s tail vertebrae
are joined together to provide the needed rigidity,
strength, and stability. Birds use their tail to help them steer
through the air. While a bird can still fly without a tail, their
flight is usually shorter and not as smooth.
What advantage do birds’ bones give them
for flight
Flight requires a lot of energy and oxygen. Birds eat insects,
nectar, fish, meats, or other high-energy foods. They also have
a large, efficient heart and a specialized respiratory system. A
bird’s lungs connect to air sacs that provide a constant supply
of oxygen to the blood and make the bird more lightweight.
Slow-motion video shows that birds beat their wings up and
down as well as forward and back. A combination of wing
shape, surface area, air speed, and angle of the wing to the moving
air, along with wing movements, provide an upward push
that is needed for the flight of a bald eagle, as shown in Figure 13.
Inventors of the first flying machines, such as gliders, used the
body plan of birds as a model for flight. As wind passes above
and below the wing, it creates lift. Lift is what allows birds, as
well as planes, to stay in flight.
542 CHAPTER 18 Vertebrate Animals
(l)Jeff Lepore/Photo Researchers, (r)Arthur R. Hill/Visuals Unlimited