Keeping Company

Crows, sociable and intelligent, are the focus of several studies at the Lab

By Sean Serrell

An adult American Crow preens a juvenile. Photo by Kevin J. McGowan

When the Lab's Kevin McGowan visits the territory of an American Crow family in Ithaca, New York, his approaching car is often announced by tagged crows flying in circles and watching from treetops, alerting one another to his annual spring arrival. Although he does not present the real threat to their nests that a raccoon or a Great Horned Owl would, crows will not hesitate to harass him, sometimes in multifamily mobs of 75 to 100 birds, as he climbs the nest tree to "borrow" a brood of nestlings for measurement and banding. American Crows have a reputation for being social and intelligent, but the abilities to cooperate to this degree and to recognize a specific car and link it to its owner are only two items in this bird’s well-stocked bag of tricks.

In fact, there is still much to be learned about what crows can do, and especially where, when, and why. For example, many populations of crows breed cooperatively, which means that offspring from previous years’ broods (who become reproductively mature at between one and two years of age) will help raise their younger siblings, sometimes staying on their parents’ territory for five or more years. Depending on the number of these "helpers," crow families can have 10 or more members. However, crows from different populations are not equally cooperative: four out of five Ithaca families have at least one helper, while Carolee Caffrey, a biologist at Audubon, found that more than 60 percent of breeding pairs in Encino, California, had none. The more we know about how much crows cooperate and in which environments, the more insight we will gain into behaviors that appear to be unselfish.

Crows Count, one of four new projects in the Lab’s Urban Bird Studies, will gather data from citizen scientists on seasonal fluctuation in family and urban roost group size, as well as on behaviors such as fighting, food caching, anting, and standing sentinel. This information will help scientists compare geographical variations in group interactions within this widespread and abundant species.

Populations exist year-round in most of the United States, but throughout central Canada and in parts of the western states, crows are present only during the breeding season. Families spend less time on territories in the winter, opting to roost communally in groups of up to one million members—long-distance migrants as well as crows from nearby areas. When these large groups gather in cities, they can create enough droppings and noise to be regarded as pests and treated accordingly. Last February, a weekend "crow shoot" competition on the outskirts of Auburn, New York, resulted in the deaths of 348 crows.

Although crows may now be a common city sight, they only began populating urban areas in the 1950s. This may be related to the widespread passage of legislation banning the use of firearms within city limits, which occurred around the same time. McGowan has found that urban crows have higher nest success than rural crows. Although each nest produces fewer and smaller offspring, the urban young seem more likely to thrive, probably because there are fewer predators.

Possibly the biggest threat to American Crow populations is West Nile virus. The illness strikes them hard and fast, so they are a good indicator species for areas likely to be hot spots for the virus. Programs like Urban Bird Studies and Project FeederWatch will be useful in tracking local and regional changes in crow populations because of West Nile virus, urban sprawl, and other factors.

HOW TO GET INVOLVED

• Study crows by joining Urban Bird Studies
• Participate in Project FeederWatch
• Submit crow counts to eBird

For permission to reprint all or part of this article, please contact Miyoko Chu, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-2451. email: mcc37@cornell.edu