by John Hadidian, Ph.D.
Look around your neighborhood; you'll probably see crows in
trees or on the ground. Now check nearby parking lots and
schoolyards. Crows are nearly everywhere you look. The 12-acre
stretch of woods behind my house is no exception. A mixture of
old and young trees that were allowed to reclaim what must have
been farm land not so long ago, it has become good habitat for
a variety of creatures and an especially good area for large
numbers of birds. The crows vigorously patrol the small,
pole-sized red maples that have spread out over much of the
land, though occasionally they just sit and watch—sometimes one
crow alone, more often in small groups.
On one side of the old farm field is a crow roost in a grove
of evergreen trees. It is mostly used in winter, and I've often
walked down in the evening to see several hundred birds milling
and settling, seeming raucous and disorganized. The roosts that
are appearing more frequently in suburban and urban areas often
hold thousands or even tens of thousands of birds. We cannot
look around our neighborhoods without noticing them, yet most
of us don't really know the crows we see.
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.
The Social Life of Crows
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 1/2
years old. The groups of crows in your backyard are extended
families, usually numbering six to nine, who will 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
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. I often hear crows cawing
to one another from some distance, in a series of vocalizations
that seem to keep the birds apprised of what is going on over a
fairly wide area. The mobbing calls are hard to distinguish
because they often sound just like more intense and higher
pitched variants of the normal caw.
A Helpful Bird
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 by no means makes
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.
Moving to the City
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 out 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.
As more municipalities identify concerns about certain
roosting areas, The HSUS will be working to promote the use of
nonlethal strategies to deter crows early in the roosting
season. There are proven techniques of hazing, harassment, and
site modification that can effectively prevent conflicts before
they occur; they simply need to be promoted and properly
implemented. Then we can settle back to enjoying a peaceful
coexistence with this complex and amazing wild bird
neighbor.
John Hadidian is director of The
HSUS Urban Wildlife Program
