Something to Crow About
An expert on the behavior of the American crow, one of our most familiar avian neighbors, answers some frequently asked questions about the bird and its natural history
IN THE HEART of insect bite season, here's a reason to envy the crested auklet: The birds create their own bug repellent. Researchers from the University of Alaska-Fairbanks discovered that when the seabirds nuzzle potential mates, they are not merely courting; they are also transferring a citrus-scented secretion that includes chemicals called THE AMERICAN CROW, which ranges across most of North America from central Canada to the Gulf Coast, is among the largest, noisiest, most common and most social birds that visit urban environs, and its numbers in some cities seem to be increasing. We asked Kevin McGowan, a Cornell University ornithologist who has been studying American crows in the Ithaca, New York, area since the 1980s, to answer some questions about the birds. His answers provide a primer on crow behavior.
How intelligent are crows?
As birds go, some crows are very intelligent. A species found on the South Pacific island of New Caledonia manufactures and uses tools from objects such as twigs. American crows also use tools and are adept at learning new tricks, such as getting food out of plastic garbage bags.
Do crows always travel in groups?
On their territories, crows tend to forage and move around in family units consisting of a mated pair and young from up to several breeding seasons. Young birds may help with nest building, rearing younger siblings and standing guard at nests and feeding sites. Young mature birds eventually set out on their own to start their own families, although some crows may stay at home for up to seven years. Crows travel in groups while away from home territories, too. They congregate with crows other than their family members to forage and sleep.
What is a group of crows called?
The poetic term used in literature is a “murder.” Scientists would call them a flock.
Why do crows congregate in large numbers to sleep?
Crows take this approach primarily in fall and winter. Roost size ranges from fewer than 100 individuals to hundreds of thousands. One site in Fort Cobb, Oklahoma, holds an estimated 2 million crows. Why they sleep in large groups is largely a matter of conjecture. They may all be attracted to one spot that offers advantages such as protection from predators and weather. Roosts also may be located near a large food source. The congregations probably serve some as yet unknown social function as well. Not all crows join these groups, and many sleep at home with just their families near them.
Why do crows roost in cities?
Urban living offers crows several possible advantages. Cities are often 5 to 10 degrees F warmer than rural areas, an advantage in cold weather, and may offer protection from human hunters. Great horned owls, which frequently prey on crows, presumably number fewer in urban areas. Artificial light may assist crows in watching for owls at night, and cities may provide some of the largest roost trees in a given area.
Why do crows fight each other?
Crows may fight for a number of reasons, such as defending territorial boundaries or some other resource or protecting their mates (or sexual access to them). Conflicts within a family are usually short and involve only a few pecks. Fights between members of different families, however, can be protracted and deadly.
Do crows mate for life?
Yes. Unless a mate is killed or severely incapacitated, crows appear to stay with the same mate year after year. It is possible, however, for exceptions to occur. A pair of young crows that mated but bred unsuccessfully might try again with other birds.
Which crows build nests?
American crow nests are bulky, constructed of an outer basket of sticks, a filling of mud and grass, and a thick bowl of something soft. In the beginning stages of construction, both members of a pair, and often some helpers, work equally hard. In fact, the male can be more active getting started. The breeding female, though, usually does the most building at the end, when they are lining the nest.
How many young can a crow family produce in one year?
Raising a crow from egg to adult usually takes about 4 months, giving adults little chance to raise more than one brood. Nest success in my New York study on crow social behavior averages 50 percent, with rural nests producing on average four young per successful nest and urban nests, three.
How long do crows live?
Most don’t live even a year, dying as nestlings or even before hatching, but a crow that survives its first year has a good chance of living for several more. The oldest reported wild American crow was 29.5 years old, although that record is disputed. The oldest crow in my study died at 16 years old, and several others have reached 14 and 15 years. A crow that spent its entire life in captivity recently died at the age of 59.
Do crows migrate?
American crows in the southern parts of the species’ range appear to be nonmigratory, although they may make changes in their use of space as seasons shift, spending more time in winter to forage and roost away from individual territories. Crows do migrate out of the northernmost parts of the species’ range, particularly from areas where the minimum January temperature averages 0 degrees F. In the middle latitudes of the United States, some members of a family may move in winter, but the breeders stay put.
How can you attract crows?
Crows have an endearing characteristic that apparently is not shared by other birds—they can identify people as individuals. While you can get chickadees to eat out of your hand, any old hand will do, and I suspect the chickadees do not know you as an individual. Crows will! If you toss them peanuts (preferably unsalted, in the shell) on a regular basis, they will wait and watch for you. Not just any person, but you. If you do this often enough, they will follow you down the street to get more, even if you’re in your car.
Is West Nile virus affecting crow numbers and is it a threat to people?
American crows are especially vulnerable to the West Nile virus, and their populations have been hard hit in some areas, such as the Midwest. In other areas the losses were quickly compensated for by the movement of helpers into breeding positions and by subsequent reproduction. West Nile virus remains a potential threat to both birds and people, and further outbreaks can be expected in the future, although perhaps at lower intensities. The presence of dead crows remains one of the first signs of a potential outbreak.
For more details, visit www.birds.cornell.edu/crows/crowfaq.htm.
The Crow: A Brainy Bird
How smart are crows? When that question was posed on Cornell University ornithologist Kevin McCowan’s website—which was the basis of the crow article in the August/September 2008 issue of National Wildlife—McCowen responded: Smarter than many undergraduates, but probably not as smart as ravens.
Other sources of information also indicate that crows aren’t exactly bird brains. Recent research on crows in New Caledonia, an island in the South Pacific, has revealed that the birds fashion twigs and leaves into several types of hooks and serrated tools for use as probes in prying insects out of hidden recesses and that the birds carry tools from site to site for reuse. In experiments with captive crows, scientists at the University of Auckland in New Zealand found that the birds would use a small stick to pull in a longer stick placed out of their reach but that was needed to dig food out of a deep hole—in other words, the birds used a tool to get a tool. In this behavior, says University of Auckland biologist Russell Gray, crows are matching the tool-using skills of great apes.—Roger Di Dilvestro
ldehydes, which repel ticks and other insects. To read more about Pacific seabirds, see this issue's feature "Seabird Signals."