A
bird moving along a telephone wire does not walk like a
tightrope artist; instead, the bird will "sidestep,"
"switch-sidle," or "hop." Sidestepping (the way that people
typically move along a ledge) involves alternately lifting
each foot and moving it to the side while continuing to keep
the same foot ahead. Switch-sidling means moving to the
right or to the left by crossing one foot over the other in
an exaggerated "pigeon-toed" step. Hopping, of course,
requires moving both feet simultaneously. When unconstrained by such a
narrow perch, many birds walk or run using the alternating
strides typical of most bipeds. Others, particularly small,
arboreally inclined species, commonly hop. It is uncertain
why hopping is more common in smaller birds. The evidence
seems to point to economy of effort: short-legged birds move
farther in a single hop than they do taking several steps,
whereas it is more economical for larger birds, with longer
strides, to move one leg at a time. Although birds of the same
taxonomic groups frequently share a common pattern of
locomotion on the ground, the patterns often have
exceptions. Most passerines hop, but others, such as larks,
pipits, starlings, and meadowlarks, typically stride. Within
the family Corvidae, jays hop whereas crows stride. Diverse
species, including robins, ravens, and blackbirds, both hop
and stride. Whether a physically unconstrained bird hops or
strides is not just a question of anatomy; speed also
affects choice of locomotion -- a hopper in a hurry tends to
break into a run. Leg length is not only
related to locomotory mode but also associated, among other
things, with foraging style. For example, among ground
gleaners and waders, species with shorter legs forage in
shallower debris or water. Some ground foragers (especially
buntings, towhees, juncos, and sparrows) are more likely to
use a method of foraging called "double-scratching," a
maneuver involving little more than hopping in place. But
here, too, there is no simple division between birds that
hop, stride, and double-scratch. Some striders
double-scratch and some hoppers do not. Recording the locomotory
patterns in local bird species in different circumstances
could be helpful in determining, for example, the conditions
under which birds that typically hop when on perches (such
as jays, flickers, and House Sparrows) continue to hop when
on the ground and under which conditions they do
not. SEE: Feet;
Visual
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How
Do We Find Out About Bird Biology? Copyright
® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl
Wheye.