Graphics Reference
In-Depth Information
Some owls depend on their acute sense of hearing for success in hunting.
This has resulted in the rounded shape of the barn owl's wing and the way
its the feathers are arranged to enable the bird to fly in almost complete
silence—as mentioned earlier, not so the prey is unable to hear the
approach of the owl but rather for the owl to hear the movement of the
small mammals on which they prey.
Seabirds
Seabirds exist mostly on a diet of fish and have developed a number of
techniques to catch them: They dive, they swim, and some skim the surface.
This has resulted in different physiognomies among seabirds. With its short
wings and fat, rounded body, the puffin is not an elegant flyer, but it swims
superbly. Gannets are more elongated and streamlined, making them more
suited to diving, which they do from a great height in order to catch fish.
Some seabirds fish on or just below the water's surface; others manage to go a
little deeper, a few meters; still others are capable of diving to greater depths.
Gannets begin their dive from high above the water; turning downward,
they power toward the surface before folding their wings fully back a split
second before plummeting into the water. This action reduces drag and
therefore allows them to dive to greater depths. What enables them to dive
so effectively hampers them underwater, however, and these birds at least
cannot swim to any great extent.
Other Birds
It would seem that design solutions in nature are always something of a
compromise when two or more conflicting needs must be satisfied; the need
for some birds to both swim and fly throws up some interesting results. The
prioritization of needs within individual species has determined aspects of
locomotion and subsequent changes to bird physiognomy that reflect this
prioritization. Extreme cases where swimming has become the priority over
the need to fly have resulted in the bird becoming entirely flightless, the price
paid to become a consummate swimmer. The penguin is perhaps the prime
example here; it's hardly capable of walking on the ground, but once in the
water it is capable of great turns of speed and maneuverability. Other species
retain the capacity for flying, though they are perhaps less well suited to
swimming. The puffin
Fratercula arctica
is perhaps a good example of the way
there is a balanced compromise between the two driving factors. Retaining
the ability to fly very well, the puffin has a body shape and wing size that
also make it very suited to swimming underwater to catch the sand eels it
feeds on.
Other birds have made less of a compromise. Ostriches have become entirely
flightless and have developed into grazers, rather like the quadrupeds with
which they often share their environment. The number of toes on the ostrich
has been reduced to two very powerful ones that are incapable of perching
