Graphics Reference
In-Depth Information
feeds by grazing on the surface of the water; some ducks such as the mallard
Anas platyrhynchos
and swans may also feed below the water by extending
their necks underwater and dabbling, even occasionally upending, to feed at
greater depths. A number of ducks dive to exploit deeper water. For ducks that
live on a diet of fish, such as the goosander
Mergus merganser
, the ability to
dive and swim has become an essential part of life. To do this efficiently, loons
and divers such as the black-throated diver
Gavia arctica
have developed legs
located much further toward the rear of the body. Though this structure makes
for great difficulties on land, it is a great aid in swimming, enabling these birds
to swim at great speed and dive to depths of 200 feet.
We have already seen how webbed feet are of immense use in swimming,
but their use as paddles is not the only method of propulsion. Though not
water birds in the same way as ducks, geese, or swans, the dipper
Cinclus
cinclus
manages to catch its meals by swimming below the surface of fast-
flowing mountain streams and rivers. In appearance it is not unlike many
birds one finds in gardens; its unwebbed feet with four long toes terminating
in curved claws are more suited to perching than paddling. Perhaps it is more
correct to say that the dipper
lies
under water rather than swims, for instead
of using its feet for propulsion it uses its wings much in the same way it uses
them to fly.
Similarly, kingfishers—though hardly classified as water birds—do depend
on water for their existence and spend a great deal of time in and around
it. They don't swim on the water's surface the same way waterfowl do, nor
do they swim underwater as dippers do, but they are expert divers. Using
an overhanging branch of a tree, kingfishers perch overlooking the water in
which they hunt their prey, fish. They dive in head first to grab a fish with their
long and rather thick, straight beak, turn, and then launch themselves from
the water's surface to return to their branch. They are adept at handling a fish
once out of the water; with a flick of their heads they stun the fish against the
branch before quickly turning it to swallow it head first so that the fish's scales
do not catch in its throat.
Wading Birds
Even though the birds that fall into the category of waders may vary a great
deal in size and habits, I have separated them out for special attention
because of the common solutions that nature has come up with to assist
them in exploiting the environment. Waders are birds that have developed
long legs, often coupled with long necks and long beaks, to exploit the
shallow water at the edge of the ocean or still water. There is even a good
deal of variation in the designs of wading birds that allow them to exploit
the various aspects of the shoreline and inland waterways and avoid any
unnecessary competition for food.
The differences in some instances, though not large, are enough to ensure
suitability for collecting particular foodstuffs from a particular place on the
