[Illustration]
The obvious adaptation of a bird's wings is for locomotion; to fly in
the air. It is true that some few birds are flightless, and some like
the penguins use their wings for underwater swimming, but this does not
spoil the generalization.
Secondary uses, some with special adaptations, occur: the owl at bay
spreads its wings wide, with the effect of increasing its apparent size
and being more terrifying to a predator. The young bird, begging to be
fed, flutters its wings in a characteristic way, and the female, in
some of her mating behavior, may also flutter her wings like those of a
young bird.
In courtship the wings may play an important part in display. In the
Australian rifle bird they are held out, fully spread on each side of
the bird like a velvet curtain against which the vivid iridescence
of the throat patch stands out more vividly. The argus pheasant has
the inner secondaries greatly elongated and ornamented in a fashion
recalling the decoration of a peacock's tail and these he spreads to
show in his courtship, while the ruffed grouse uses his wings to make
instrumental music, his drumming.
Wings in geese and swans may be used in fighting, and tame birds may
severely buffet humans who take too close an interest in their young.
In the related screamers of South America the bend of the wing is
equipped with long, very sharp spurs, which undoubtedly make formidable
weapons in fighting.
In addition wings are used in at least three different ways in feeding.
The red-tailed hawk may spread its wings as it sits on its prey,
perhaps a behavior adapted to help the bird maintain its balance when
dealing with struggling prey, perhaps to help smother the struggles of
its prey.
The secretary bird of Africa is said to feed on snakes, poisonous and
non-poisonous ones, and is said to use its huge wings as shields for
its body in attacking them.
But the strangest use of wings in feeding is that practiced by a
blackish African heron. In feeding in shallow water it takes a few
rapid steps, apparently to bring it within reach of fish it has
sighted, then spreads its wings, bringing them forward until they
meet, and with the tips of the quills in the water. The head is in
the canopy formed by the wings, and apparently it is here under this
canopy that the fish on which it feeds are caught. The suggestion as
to the correlation that presents itself is that the dark canopy thrown
over the fish confuses them and makes them easier to catch.