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Bob Rosenfield holds a pair of Cooper’s hawks in a city park in Victoria, Canada. The female, in the foreground, is a third again as large as her mate. (Eric Wagner)

The Hawks in Your Backyard

Biologists scale city trees to bag a surprisingly urban species, the Cooper's Hawk

Bob Rosenfield stares up into the high canopy of a Douglas fir in Joanie Wenman’s backyard, in the suburbs of Victoria, British Columbia. “Where’s the nest again?” he asks.

“It’s the dark spot near the top, about 100 feet or so up,” says Andy Stewart. “The first good branch is around 70 feet,” he adds helpfully.

“All right!” Rosenfield says. “Let’s go get the kids.” He straps on a pair of steel spurs and hefts a coil of thick rope. Hugging the tree—his arms barely reach a third of the way around it—he starts to climb, and soon falls into a labored rhythm: chunk-chunk as the spurs bite into the furrowed bark; gaze up; scout a route; feel for a grip with his fingertips; hug the trunk, chunk-chunk. Those of us pacing beneath listen to him grunt and huff. As he nears the nest, the female Cooper’s hawk dives at him with an increasing, screeching fervor: kak-kak-kak-kak-kak!

“Woah!” Rosenfield yells. “Boy, she’s mad!”

“Man, I hate watching him do this,” Stewart mutters. Most people, he says (his tone implies he means most “sane” people), would use a climbing lanyard or some other safety device should they, say, get thumped on the head by an irate Cooper’s hawk and lose their grip and fall. “But not Bob.”

At last, Rosenfield reaches the nest. “We got four chicks!” he calls down. “Two males, two females!” He rounds them up (“C’mere, you!”) and puts them in an old backpack. He uses the rope to lower the chicks to the ground. Stewart gathers up the backpack and takes the chicks to a large stump. They are about 19 days old, judging by the hint of mature feathers emerging from their down. He weighs them, measures the lengths of their various appendages and draws a little blood for DNA typing.

Meanwhile, Rosenfield stays in the canopy, gazing off into the middle distance. After the chicks have been hoisted back to the nest, I ask Stewart what Rosenfield does while he waits. “I don’t know for sure,” Stewart says. He chuckles. “I think he likes to watch the hawks fly underneath him.”

Rosenfield, a biologist at the University of Wisconsin, Stevens Point, has been free-climbing absurdly tall trees in pursuit of Cooper’s hawks for more than 30 years. Cooper’s hawks are about the size of a crow, although females are a third again as large as males, a size disparity apparent even in chicks. The sexes otherwise look alike, with a slate back, piercing red eyes and russet-streaked breast, the exact color of which varies with geography. Rosenfield has worked with other, perhaps more superficially impressive species in more superficially impressive places—gyrfalcons in Alaska, peregrine falcons in Greenland. But even though he’s most likely to study Cooper’s hawks in a city, he has a special fondness for them. “They’re addicting,” he says. “DNA really outdid itself when it figured out how to make a Cooper’s hawk.”

Not everyone thinks so. With their short, rounded wings and long tail, Cooper’s hawks are well adapted to zip and dodge through tangled branches and thick underbrush in pursuit of prey. They occasionally eat small mammals, like chipmunks or rats, but their preferred quarry is birds. Cooper’s hawks were the original chicken hawks, so called by American colonists because of their taste for unattended poultry. Now they are more likely to offend by snatching a songbird from a backyard birdfeeder, and feelings can be raw. After a local newspaper ran a story about the Victoria project, Stewart received a letter detailing the Cooper’s hawk’s many sins. “Two pages,” he says. “Front and back.”

Due in part to such antipathy, Cooper’s hawks were heavily persecuted in the past. Before 1940, some researchers estimate, as many as half of all first-year birds were shot. In the eastern United States, leg bands from hawks that had been shot were returned to wildlife managers at rates higher than those of ducks, “and it’s legal to hunt those,” Rosenfield says. Heavy pesticide use in the 1940s and ’50s likely led to eggshell thinning, which further depleted populations. On top of that, much of the birds’ forest habitat was lost to logging and development. The species’ predicament was thought so dire that, in 1974, National Geographic published an article asking, “Can the Cooper’s Hawk Survive?”

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