Crows Cope With Family Values, City Living, and West Nile Virus
April 20, 2009
One of the brainiest birds on the planet is also one of the most misunderstood—the American Crow. But the more you learn about these birds, the more you realize how interesting they are and how much we have to learn about them. By studying crows, researchers at the Cornell Lab of Ornithology have revealed fascinating information about these adaptable, family-oriented birds. In some respects, crows and humans seem to have a lot in common—including sociable lives and a fondness for junk food.
Crow Family Values
Cornell Lab researcher Kevin McGowan has been studying crows for two decades—the last 10 years with collaborator Dr. Anne B. Clark and her graduate students at Binghamton University. McGowan and Clark have tracked the dynamics of crow families across generations. In some cases, offspring from previous years stick around to help raise their younger siblings. “They help feed the female on her nest, feed the nestlings and fledglings, defend the territory and the nest, and stand guard over other family members while they hunt for food,” says McGowan. “This kind of cooperative breeding behavior is rare in birds.”
The younger birds may stay with their parents for five or more years and families may include up to 15 individuals, sometimes including step-parents and their children, nephews, brothers, or even unrelated birds. McGowan has also observed cases of “adoption.” After West Nile virus killed a crow known as “RV” and a neighboring pair, his mate adopted the neighbors’ orphans. Later, the orphans helped their adoptive mother raise her young.
Crows and West Nile Virus
Crows got more than their usual share of attention when West Nile virus made its first appearance in New York City in summer 1999. Crows are extremely vulnerable to the illness and nearly 5,500 crows died in just 4 months. Although the virus took a huge toll at first, crow populations appear to be bouncing back somewhat. Using data from the North American Breeding Bird Survey, Cornell Lab scientists found in 2010 that West Nile virus became less virulent as it moved westward across North America. They also found that crows in diverse habitats were less likely to come down with the disease. “That’s a finding of some environmental interest,” says Cornell Lab senior scientist Walter Koenig, who led the study. “It implies that diverse ecosystems are better able to mitigate some pathogens’ effects on highly sensitive species.”
Life in the City
Because crows are adaptable, they often thrive near people. Each year, the Cornell Lab receives many inquiries about crows as a “nuisance” when large groups gather in the neighborhood each night in fall and winter as they go to roost. Some crow roosts can swell to more than a million birds. When people complain, McGowan shares a different perspective. “Roosting is simply instinctive crow behavior and I think it’s one of the marvels of nature,” he says. “We’re not 100 percent sure why they do it, but it seems to have something to do with safety in numbers.” The birds start dispersing again at the start of the breeding season, usually in March.
Safety is another reason crows may like city living so much. McGowan’s research shows that urban crows have smaller offspring than rural crows, but the urban youngsters are more likely to survive because there are fewer predators. Crows will eat just about anything, so they may also prefer the buffet choices available in cities including garbage, pizza, and French fries. However, just as for humans, it’s not the best choice. Binghamton University graduate student Rebecca Heiss did a study on the Ithaca crows’ diet. She found the urban food crows ate was of much poorer quality than that found in rural areas.
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Crows in a New Light
Crows are often misunderstood. The literary term”murder of crows,” to describe a flock, hints at something sinister about them. McGowan thinks a better understanding of crows would help people see groups of crows as families, not gangs. “People attribute some sort of malicious intent to what crows do when they’re just trying to raise their kids like everybody else,” he says. “It would be nice if people actually thought about it as mom and dad and the kids from last year who are still helping them raise young. It’s not a bunch of juvenile delinquents coming through and trying to cause trouble.”