Look around your yard. You'll probably see crows in trees or on
the ground. Now look at nearby parking lots and school yards.
These large black birds are nearly everywhere, but how much do
you really know about crows?
The Clever Corvid
Crows belong to the family Corvidae, a grouping that
includes ravens, magpies, and jays. Of American birds, crows
are thought to be among the most intelligent and social.
Scientists have observed them making leaf and twig tools and
using those tools to catch insects. Crows plan ahead, hiding
food in crevices in tree bark and on the ground in dry grass
and leaves. If snow covers their caches, crows have no trouble
recovering them.
Crows tend to mate for life. Offspring spend up to six years
with their parents, helping to care for subsequent nestlings
and learning parenting skills. Most crows do not survive past
the first year of life. Those who do survive often live 17
years or more. (The oldest known wild American crow was 29
years old.) The groups of crows in your backyard are extended
families, usually numbering six to nine, which gather into
larger groups to roost, a practice that protects them from
predators.
Crows work together to mob a threatening predator or another
crow attempting to move in on the group's territory. One crow
will sound an assembly call, the flock will gather, and the
group will pursue and surround the interloper, cawing loudly in
unison.
Caw-caw is the sound most people associate with the
crow, but it is just one of the bird's approximately 25
rattles, clicks, and bell-like tones. The caws themselves can
vary in pitch, intensity, and number, suggesting a fairly
sophisticated level of communication. The mobbing calls are
hard to distinguish because they often sound just like more
intense and higher pitched variants of the normal caw.
A single family of crows can consume 40,000 grubs,
caterpillars, army worms, and other insects in one nesting
season. Twenty percent of the Eastern crow's diet consists of
insects that are generally considered pests by gardeners and
farmers. Though crows do eat corn, the grain does not make up a
large percentage of their diet, and the amount of corn they
consume is offset by the good they do for crops by eating
damaging insects and larvae.
Crows are good citizens of their ecosystem; their seed
transport and storage contribute to the maintenance, renewal,
and spread of forests, thereby stemming soil erosion. And their
habit of eating carrion makes them nature's cleanup crew.
Urban Dwellers
The last three decades have seen a dramatic shift in the
roosting patterns of crows. Large numbers of crows throughout
the U.S. have apparently decided that urban roosts are more to
their liking than those in the country. As the sun begins to
set on a typical winter evening, thousands of crows can be seen
streaming into urban woodlots, yards, and shopping centers. Why
they have changed their habits so remarkably remains to be
determined. We know, because of the "heat island" effect, that
inner cities are typically warmer than the hinterlands. Perhaps
it is warmth that these birds seek, or perhaps they are seeking
freedom from predators such as owls.
These newly urban crows may have equal cause for concern
about an emerging enemy: humans. Urban residents are beginning
to call for the control of urban crow roosts. Too many birds,
too much mess, too much noise, and too little tolerance may
bode ill for crows, as municipalities with roosts hastily look
to lethal control programs rather than humane approaches that
offer long-term solutions.
