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takeoff simply by leaping from the ground into the air to gain the necessary
momentum because they require less initial thrust to get airborne. Clearly,
jumping to become airborne works well only if the bird is below a certain size.
Birds a little bigger than a pigeon find that the huge wing beats required for
this kind of takeoff are very difficult; larger birds find it impossible and have
had to develop other ways of becoming airborne.
Taking of from the branch of a tree or other kind of perches may require
nothing more from the bird than simply allowing itself to fall away from its
perch. Pigeons and seabirds regularly take off from a cliff face or the side
of a building by simply dropping or pushing away from the surface. The
momentum from the fall alone is enough to create sufficient air speed over
the surface of the wing to gather the necessary lift.
FIG 4.53 Small passerine (starling)
taking off from a perch.
Larger birds might need to run or taxi to generate sufficient airflow over the wing
to become airborne, or they get airborne from an elevated position such as a cliff
face. Facing into the wind helps with takeoff because the airspeed provided by
the wind brings with it a degree of lift. In some exposed positions such as at the
top of high buildings or cliffs, takeoff may simply be a matter of a bird extending
its wings and allowing the breeze to provide all the lift that's required.
Taxiing is a method of takeoff that's more suited to large birds with large
wings. They run along the ground or water with outstretched wings, much the
same way that aircraft travel along a runway gathering speed. Swans provide
FIG 4.54 Large water birds take off
by taxiing.
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