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Bird Beaks and Feet
Nature Bulletin No. 595-A March 13, 1976
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation
BIRD BEAKS AND FEET
A bird is essentially a lizard which has been rebuilt into a flying
machine. During this remodeling its teeth were lost, most of its reptilian
scales were elaborated into feathers, the long whip-like tail shrunk to a
mere knob, and the forelegs were sacrificed to make wings.
The circumstantial evidence that birds are descended from lizards was
given strong support by the discovery of a fossilized "missing link"
named Archaeopteryx, "old winged-one. " This creature lived about
125 million years ago. It had jaws with pointed teeth but no hard bill.
The fore limbs were partly feathered wings but each had three free
fingers with claws. The long lizard-like tail had twenty vertebrae, each
with a pair of large tail feathers. Were it not for the clear imprint of
feathers in the rock, it would have been called a reptile.
Birds
have developed many ways to use their beaks and feet to take the
place of hands. For example, several times each day, brooding parent
birds of all kinds use their bills to turn the eggs beneath them. Also, a
young bird has a small sharp egg tooth, near the tip of its upper bill,
with which it chips its way out of the egg shell. Soon after hatching this
egg tooth drops off.
The type of bill on a bird gives a good clue to its feeding habits.
Carnivorous birds like hawks, owls and eagles have strong hooked
beaks for tearing flesh. Herons, egrets and kingfishers, with their
straight heavy bills, spear fish, frogs, and crayfish -- then gulp them
down head foremost. Ducks and geese dredge up roots, seeds and small
water life, letting the mud and water strain away through grooves in the
edges of their broad shovel-like bills. The woodcock probes in damp
soil for earthworms with its long slender bill. The hummingbird uses its
long proboscis to suck up nectar. The short stout cone-shaped beaks of
such birds as the cardinal and the sparrows are adapted for gathering
and cracking seeds.
Most songbirds feed protein-rich insects to their growing young. Some
use specialized bills for this job; others do not. The warblers have thin
tweezers for picking small insect life from vegetation. Swallows, swifts
and night hawks are flying "insect nets " that can open wide gaping
mouths for scooping up food on the wing. The woodpeckers have
chisel-bills that hammer holes in dead wood for grubs which they
harpoon with their long barbed tongues. These bills are equipped with a
special shock absorber that prevents injury to the brain.
The beak is used to carry selected nest materials and to construct a
certain characteristic type of nest. Hawks and eagles, however, carry
nest sticks with their feet. So does the little chimney swift which snaps
off dead twigs on the fly and glues them with saliva into a cup nest deep
inside an unused chimney.
A bird's feet also indicate its habits. Webs between the toes are found
on ducks, geese and other swimmers. Wading birds have long legs and
toes. Hawks, eagles and owls have powerful feet with long curved
talons for seizing prey and piercing its vitals. Perching birds have a
special ligament which automatically locks their toes around the perch
when they sit down to sleep.
Birds
of all kinds seem to spend hours preening their feathers,
sometimes with their bills and sometimes with their feet. In this way
they relink the thousands of microscopic hooklets which hold together
the filaments of each feather.
Their scaly legs and toes remind us of their lizard ancestry.
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