Grebes are members of
the Podicipediformes, a widely distributed order of freshwater
diving birds, some of which visit the sea when migrating and in
winter. Grebes are small to medium-large in size, have lobed toes,
and are excellent swimmers and divers. However, they have their
feet placed far back on the body, making them quite ungainly on
land. They leave the water only to nest, walking very short distances
upright like penguins. They can run for a short distance, but
often fall over. Grebes have narrow wings, and some species are
reluctant to fly; indeed, two South American species are completely
flightless. They respond to danger by diving rather than flying,
and are in any case much less wary than ducks. However, the North
American and Eurasian species are all, of necessity, migratory
over much or all of their ranges, and those species that winter
at sea are also seen regularly in flight.
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Even the small
freshwater Pied-billed Grebe of North America has occurred as
a transatlantic vagrant to Europe on more than 30 occasions. Bills
vary from short and thick to long and pointed; the feet are always
large, with broad lobes on the toes and small webs connecting
the front three toes. The hind toe also has a small lobe. Recent
experimental work has shown that these lobes work like the hydrofoil
blades of a propeller. Curiously, the same mechanism seems to
have evolved independently in the extinct Cretaceous-age Hesperornithiformes.
Grebes have unusual
plumage. It is dense and waterproof, and on the underside the
feathers are at right-angles to the skin, sticking straight out
to begin with and curling at the tip. By pressing their feathers
against the body, grebes can adjust their buoyancy. Often, they
swim low in the water with just the head and neck exposed.
Above Images From The U.S. Fish and Wildlife Service
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