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rule can be seen in the behavior of penguins, which do exactly that during the
long Antarctic winters.
Water Birds
A great number of birds other than specialist seabirds have taken to life
on and in the water. Many of these exhibit adaptations to this way of life.
Perhaps the most obvious one is the development of the webbed foot
that allows for propulsion on both the water's surface and underwater.
The body shape of water birds is generally elongated and broad; they
have long necks and their legs are set well back on their bodies to aid
swimming. The position of the legs gives these birds their distinctive walk:
a waddling gait.
Buoyancy for all water birds is a critical factor and the care of plumage to retain
waterproofing is essential. Without proper preening the feathers would become
waterlogged, making it impossible to retain the necessary buoyancy. Some
water birds have evolved to exploit and feed at different levels on and in the
water, thereby avoiding unnecessary competition. The shoveler Spatual clypeata
(a)
FIG 4.44 a: The waterproof
properties of their plumage give the
ducks great buoyancy and they ride
high in the water, unlike those that
dive to catch fish such as the great
northern diver. b: The divers' lack of
buoyancy enables them to remain
underwater for greater periods of time
to catch their prey, fish.
(b)
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