In the company of crows
Clever birds lead complex lives
To the uninitiated, the birds all look the same — shimmering black feathers, with eyes, beaks and feet to match. They sound the same, too, their calls collapsing into cacophony as they rise and fall on the wing.
Not so for behavioral ecologist Anne Clark. Binoculars at the ready, the associate professor of biological sciences sees enough intrigue and drama among a murder of crows to one day fill a novel. There is the peanut hound abandoning her nest for a treat, the devoted father driven from home in his dotage — by his sons — and the orphaned juveniles insinuating themselves into a new family. Hear the alarm call? The territorial declaration?
Clark has devoted the past decade of her research career to deciphering the biological and social relationships among a population of some 2,000 American crows in Ithaca, N.Y. “I’m interested in social behavior,” she explains, “and these birds are not only long-lived, they have a very complex social life.”
Corvus brachyrhynchos, she says, rivals even the primates to whom behavioral ecologists have traditionally turned for insights into the evolutionary underpinnings of social relationships. The ubiquitous black birds mate for life, can survive for nearly two decades in the wild and collaborate in extended family groups to rear their young. The species toggles — sometimes hourly — between strict territoriality and peaceful social groupings that can number in the tens of thousands. The combination of communication skills, memory and cognitive sophistication that makes it all possible has yielded rich fodder for Clark, collaborator Kevin McGowan of Cornell University and more than a dozen Binghamton University graduate students.
“I’m interested in complex groups that aren’t about predation or being together all the time,” says Clark, “and how individuals might follow different trajectories, navigating relationships over their lifespan.”
Complementary questions motivated McGowan back in 1990, when he began tagging and banding crows at Cornell’s Laboratory of Ornithology. The two started working together eight years later, when a student of Clark’s did some research with McGowan. These days, his post affords less time for the crows; Clark and her graduate students have filled the breach, expanding and extending the project. “I used to be in the field every day, March through June,” says the ornithologist. “I still do a lot of banding, but Anne keeps things going, keeps track of the data. Now it’s a community project.”
Watching and waiting
On a bleak morning in early January, Clark and graduate student Leah Nettle, who’s analyzing the crow’s rich repertoire of vocalizations associated with food, log three hours driving the professor’s red Subaru station wagon — “the mobile lab,” she calls it — within a 10-square-mile landscape in Ithaca’s northern suburbs. This circuit of crow territories — you and I know them as subdivisions, golf courses and office parks — has been the biologist’s field station since 2000. To reassure neighbors potentially alarmed by her binoculars and erratic driving, Clark displays a sheet of yellow paper on the dashboard. CROW RESEARCH.
With Clark behind the wheel — rarely exceeding 10 mph — Nettle scribbles observations in a journal, noting what each bird is doing, where and with whom. Occasionally, Nettle tosses a handful of unsalted peanuts, still in their shells, beside the car. The ploy yields a clear view of a bird’s wing tag as it swoops down to snatch the treat. If the researchers yearn to make a more leisurely inspection, Clark makes a few passes over the shells, crushing them with the vehicle’s tires. “They can’t pick up the pieces as easily,” she explains, “so they stay longer where we can see them.”
Crows are wary, vigilant creatures, so Clark and her team rarely emerge from their vehicles. The birds, however, seem to recognize the cars — flying nearby as the scientists proceed along their route, alighting in a tree with a view when the vehicle stops. “Now the crows that are familiar with us are very quick to figure out and respond to a new car,” Clark says. “When I first got my red Subaru in 2011, I could go incognito, stop and watch them. But I had to completely refrain from feeding anyone peanuts, because then it was all over.”
One summer, Clark’s students investigated how the crows recognized the scientists. Was it the peanuts? The slow crawl of the vehicles? Color, make or model? To find out, they used two unfamiliar cars — peanuts were tossed from one, something unappealing from the other. But the crows tasted — and returned for — everything. Then someone suggested gravel. “It was hard not to anthropomorphize, the first time they came down for the gravel,” Clark says. “They looked at us like we’d really gone nuts, like ‘They can’t possibly have meant to feed us this.’”
A natural evolution
Clark has been watching animals since childhood. Her father, a child neurologist, and mother, a pediatrician, raised Anne and her sister in rural Maryland and, later, in Lexington, Ky. Both parents were fascinated by animal behavior, and the family kept a menagerie of geese, chickens, cats, dogs, ponies, even the occasional calf. Clark was 12 when she first bought a book with her own money. Evolution, a Time-Life tome complete with full-color illustrations, still occupies a place of honor in her home library. “I read it forward and backward,” she says, “and I knew I wanted to do evolutionary biology.”
Clark was a sophomore majoring in biology at the University of Chicago when she began working with a professor on the redesign of a small Indiana zoo. Over the next 12 months, she would serve as zookeeper, education coordinator and member of its board of trustees. Among the creatures she encountered there, the bush baby — a small, proto-primate native to South Africa and known for its wide eyes, long tail and nocturnal habit — captured her imagination. As a graduate student, Clark devoted four years to the creature, crafting a dissertation on its use of scent to mark its territory. The work earned her a PhD in evolutionary biology in 1975.
That summer, she married fellow evolutionary biologist David Sloan Wilson, and the newlyweds set off for South Africa, where Clark continued her bush-baby studies. For the next decade, the tables were turned as Clark followed Wilson — first to the University of California, Davis, and then to Michigan State University. Along the way, they collaborated occasionally, investigating reproductive strategies in birds and individual variations in boldness and shyness in several species.
In 1988, the couple arrived at Binghamton, where each assumed a tenure-track professorship in the Department of Biological Sciences.
Clark has a unique capacity to integrate rich field observation into her analyses of the data she collects, says Wilson. “She knows her organism intimately as individuals and is prepared for them to tell her things, instead of imposing theories upon them. She’s often skeptical, and uses those questions to formulate new theories. That’s one of the things that I respect most about my wife.”
That and her knack for climbing a tree, well into her 60s. Every spring, as the birds begin building nests — in branches more than 80 feet above ground — McGowan and Clark muster their team, monitoring which trees have become construction sites. A month later, during the few days when chicks are big enough to be handled, but not yet bold enough to jump from the nest, the researchers don harnesses and start climbing, collecting nestlings in a bucket and lowering them to the ground to be measured, tagged and banded. A sample of blood is collected from each chick before it’s returned to the bucket and then the nest.
As Clark has documented the life histories of hundreds of hatchlings, she’s grown fond of particular birds. But because of West Nile virus, her favorites increasingly exist only in the realms of data banks and memory. In 2003, the Ithaca crow population was cut by more than a third. In 2012, 20 percent of the birds died.
The team’s notes have begun painting a picture of how family groups respond to mortality and loss. “We lost one of my personal favorites this past year,” says Clark. BT, a female hatched in 2005, “moved like a ballerina.” Her mate and their offspring disappeared around the same time, and now their family territory stands vacant.
Clark calls it the “haunted house” effect. Because crows rely on each other for information, survivors have fewer social cues available to inform territory selection.
How the birds cope with stress — on a molecular level — is the next chapter in her research. Using the combination of field notes and the thousands of blood samples she and McGovern have collected, she hopes to get a better handle on the genetic underpinnings of how the birds respond to stress. In particular, she’s interested in which crows thrive in suburban areas, where life is more crowded and noisy.
“We’re pretty sure that it involves some changes in genes associated with responses to stress, especially social stressors,” she explains, “including things having to do with learning and memory.”
Currently she’s looking at variations in DRD4, a dopamine receptor gene that, in people, is associated with responsiveness to environmental cues.
“Crows do a lot of things the way people do,” she says, noting that, like humans, the birds are cooperative, simultaneously family and group-oriented, and have a high capacity for adaptation. “It’s a really great organism to help us understand — as ecologists — how being really adaptable isn’t necessarily simple.”