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In-Depth Information
in an instant and make grabbing and holding onto a flopping fish a feasible
hunting tactic.
The ostrich foot has evolved into two large, strong toes, neither capable of
perching or holding onto prey but highly efficient for incredibly high running
speeds.
Feathers
Birds' reptilian ancestry can still be seen in the feathers that cover all modern
birds' bodies. Feathers are made of the same substance as the scales that birds
have on their legs, which is
keratin
, the same material that makes up the scales
that modern reptiles have all over their bodies. Feathers are simply modified
scales that have evolved into a more filamentous form; in so doing they have
enabled birds to achieve powered flight.
FIG 4.39
Different types of bird
feathers. a: Flight feathers (pennae).
b: Down feathers (plumulae).
There are two main types of feathers: the outer feathers (
pennae
) that define
a bird's shape and provide insulation, and an inner layer of down feathers
(
plumulae
) that provide additional insulation.
Feathers have become such a vital part of powered flight because they provide
the wing with the necessary smooth and even surface. Feathers possess a
series of interlocking barbs that enable them to form a single smooth surface,
their asymmetric shape providing the necessary shape for flight. The nature
of flight feathers remains the same for all birds, but some have been modified
depending on the birds' modes of flight. Owls have a rather fluffy edge to the
feathers that cuts down the noise of the wing beat—a valuable development
for a predator that depends on silence for its success as a hunter. This silence is
not necessary so that the prey can't hear the owl's approach; it is to allow the
owl to hear the sound of the prey over the noise of its own wing beats.
