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FIG 4.45 Differences in the wading
birds' length of leg and beak help
them exploit different food sources.
shoreline. Consequently one may see a variety of species at any one time
foraging along the shoreline. The strong, straight bill of the oystercatcher
makes it ideal for gathering mussels and other mollusks and crustaceans;
the curlew has a longer curved beak that it can use to probe mud flats
for worms and small mollusks. At half the size of the curlew, the redshank
uses its shorter beak mainly to collect insects, free-swimming shrimps, and
lugworms.
One small bird, the wrybill Anarhynchus frontalis of New Zealand, has
developed a unique feature to assist in getting food from under small stones.
It is the only bird in the world with a sideways bend in its beak. This bend
allows the bird the leverage with which it turns over small stones and pebbles
on the shoreline to reach small crustaceans, insects, and worms. Interestingly,
all wrybill beaks bend to the right.
The black heron Egretta ardesiaca , found in Africa, has a particularly neat trick
called canopy feeding to catch its prey of small fish. By extending its wings
to cover its head as a kind of umbrella, it effectively shades part of a body of
water from the glare of the sun, enabling the bird to see more clearly into the
water. This shading of the water also attracts small fish, providing them with
what they perceive as shelter and safety.
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