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Like airplanes, birds rely on lift-an
upward force that counters gravity-in order to fly.
Birds generate lift by pushing down on the air with
their wings. This action causes the air, in return,
to push the wings up. The shape of wings, which have
an upper surface that is slightly convex and a lower
surface that is concave, contributes to this effect.
To turn, birds often tilt so that one wing is higher
than the other.
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Different wing shapes adapt birds
for different styles of flight. The short, rounded
wings and strong breast muscles of quail are ideal
for short bursts of powered flight. Conversely,
the albatross's long narrow wings enable these
birds to soar effortlessly over windswept ocean
surfaces. The long, broad wings of storks, vultures,
and eagles provide excellent lift on rising air
currents.
Feathers also help to minimize
drag, a force of resistance that acts on solid
bodies moving through air. Contour feathers, which
are the most abundant type of feather, fill in
and cover angular parts of a bird's body, giving
birds a smooth, aerodynamic form.
Bird tails are also important to flight. Birds
tip their tail feathers in different directions
to achieve stability and to help change direction
while flying. When soaring, birds spread their
tail feathers to obtain more lift. When landing,
birds turn their tails downward, so that their
tails act like brakes.
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