CITY OF CROWS
Our feathered friends are increasingly calling our urban centres home. Why crows in particular are nesting among us.
ON A CLEAR morning in Vancouver, daybreak arrives with a blaze of sunlight that floods into the downtown core, igniting the glass towers of Yaletown and glinting on the sailboats moored along False Creek. It looks like a pleasant and normal winter morning until the crows appear — an undulating torrent that issues out of the rising sun and pours into the heart of the city. For almost half an hour, the crows flow by. Vancouverites have grown accustomed to these daily trips, but to a visitor, their sudden appearance is strange and intriguing. Where are all these birds coming from? And why are they here? Like the rush-hour commuters merging onto the Granville Bridge below them, the crows seem to have timetables and destinations in mind. A smaller flock of 60 splits off from the main stream and heads southwest into Kitsilano, breaking apart again into smaller family groups of six or eight birds. These groups glide into the parking lots of shopping malls and fast-food joints, head for the University of British Columbia campus, or continue toward the lawns of Kerrisdale, where they will spend the morning digging up juicy chafer grubs. As the crows get to work, they stay in touch with each other with unique squawks that each family member can recognize from blocks away. The intricate workings of crow society suggest a parallel world, a mystic society that’s beginning to draw the attention of researchers around the world.
IT’S A COMMON
belief among nature enthusiasts that suburban sprawl spells doom for wildlife. Whenever a black bear gets tranquillized in a schoolyard or a coyote kills the neighbour’s cat, the common remark is, “Well, what do we expect? We’ve invaded their natural habitat.” As with most such theories, this is only partly true. Wild animals sometimes seek out the company of people. In a number of Canadian cities, deer populations are actually much higher than in the surrounding countryside. Some cities support populations of black bears. Foxes, coyotes, raccoons, squirrels, beavers, rabbits and a wide variety of birds find much to recommend in city life, too. In 1900, a bird survey in London, England, enumerated 25 species. A second survey 75 years later showed the city had lost five species but gained 20. Other cities have seen similar changes.
These counterintuitive findings recently prompted American ornithologist John Marzluff (author of Gifts of the Crow, In the Company of Crows and
Ravens and Welcome to Subirdia) to survey his own suburban region of Seattle. He and his colleagues counted birds in undeveloped countryside and did followup surveys after those tracts had become housing subdivisions. Of the 44 species originally tallied, 10 “avoiders,” such as the Townsend’s warbler and western tanager, had declined or disappeared. “Adapters,” such as finches, sparrows and hummingbirds, had integrated well, and “exploiters,” such as wrens, mallards, swallows and Canada geese, did even better, in some instances increasing a hundredfold. All told, 34 of the original species had increased. None of these findings cast doubt on the importance of wilderness preservation. But they do demonstrate that while it’s true we are invading wildlife habitat, they are also invading ours. The fast-food restaurants, garbage dumpsters, mowed lawns, boulevard trees, wooded parks, engineered ponds and golf courses typical of Canadian suburbia make a sort of Valhalla for many birds, especially crows.
THE SAME CROWS
that pour west into downtown Vancouver every morning outside of breeding season make the reverse journey every afternoon, heading toward Burnaby. Why not just stay in Vancouver? (As one Burnaby wit quipped, “They can’t afford to live there.”) When the crows arrive in Burnaby, they settle in roosting areas on the outskirts of town. One busy roost is on the edges of Burnaby Lake. The lake teems with waterfowl, and its marshy edges look like good feeding grounds. But the multitudes of crows that swoop into the park around four in the afternoon don’t seem hungry. Local ornithologist George Clulow says it’s not exactly clear why the birds gather in these spots. “If you watch them closely as they’re walking around the mud flats, they’re mostly socializing,” says Clulow. “Crows have strong family ties. They help raise the young, and the families travel together. It’s possible that they come here to find a mate.” Crows might also use these pre-roosting areas to swap intel — the corvid equivalent of after-work pubs. Honeybees use body language to tell each other about food sources, and scientists have identified several dozen distinct crow vocalizations that, when combined with clicks and gestures, seem to form the building blocks of complex communication. To test corvid ability to pass on information, Marzluff and his graduate students donned rubber Halloween masks, live-trapped several crows, marked them with leg bands and released them onto the campus of the University of Washington. The researchers were then mobbed and scolded by different crows (in addition to the original crows) whenever they put on the same masks and walked the campus. When they wore a “neutral” disguise — in this case a mask of Dick Cheney — the crows generally ignored them. Somehow, most of the
The intricate workings of crow society suggest a parallel world, a mystic society that’s beginning to draw the attention of researchers around the world.
crows on the campus had gotten the warning about the experimenters. Marzluff also learned that crows have long memories — in one case he was harassed by a crow he’d banded 10 years earlier. How do captured crows “tell” other birds about scary researchers? Until quite recently, scientists assumed that language, information swapping, problem-solving and using tools separated humans from animals. (In the landmark 1968 film 2001: A Space Odyssey, the crucial moment in human evolution is dramatized by an ape learning to use a femur as a weapon.) But as experiments such as Marzluff’s add to a growing body of research about animal behaviour, these distinguishing criteria are falling away. Scientists are learning that octopuses can think. Dogs can feel sorrow. And parrots enjoy watching The Simpsons.
AT DUSK, THOUSANDS
of crows lift off from their roosts just outside Burnaby and head into the city, joining dense flocks from other staging areas. At an intersection in central Burnaby, vortexes of black birds whirl down out of the overcast sky, settling on rooftops, lampposts, boulevards and stop signs. To an onlooker, it seems as if the sky has cracked open and every crow on the planet is pouring onto this utterly unremarkable expanse of suburbia. Like a scene from Hitchcock’s The Birds, thousands of crows gather in fidgety masses on bare trees and crowd shoulder-to-shoulder on hydro lines. It’s not raining, but women heading home after work nevertheless grimace and hold umbrellas over their heads as they pass under the jostling crows. There may be no obvious reason why the crows come here, but Clulow says they’re clever birds, and they do everything for a reason. “They exploit every chance of survival, and they’re quick to adapt. Their choice of this spot may have something to do with the growth of Burnaby. It’s a bit warmer than the surrounding countryside, so this roost may allow them to conserve energy on a cold winter night. There’s safety in numbers, too, and any hawk, owl or raccoon that showed up here would be quickly mobbed and driven off.” Other birds (such as robins and sparrows) do well in suburbia, but they don’t form enormous and complicated societies that share information and defend against threats. Why are crows so well organized? Crow behaviour might have something to do with their intelligence. Without implying disrespect toward the typical male robin, which might spend hours hurling itself against its own reflection in a kitchen window, scientists are learning that crows are smarter than the average bird. It’s difficult to measure intelligence, even in humans, but crows get high marks among scientists for their impressive problem-solving. In one test, a crow jammed a wire rod into a crevice, then gripped the other end for maximum mechanical advantage and walked in a semicircle, bending the tip of the rod into a small hook, which it then used to extract a treat from the bottom of a tube. British researchers tested a crow that could solve a sequence of complex problems — in the right order — to get a reward. Crows can also understand symbols and analogies, and unlike a robin, they can look in a mirror and seem to understand that it’s a reflection. They also seem to know they are distinct from others. Scientists call this “theory of mind.” When crows are stashing treats, they make sure other crows aren’t watching. They comprehend that other crows may have separate and sometimes conflicting needs. (In human children, this is a major step in psychological development.) When appraising human onlookers, crows use a beady, calculating stare that some people find creepy. Marzluff has conducted experiments on corvids that determined crows have large brains compared to their body size. Brain-to-body mass ratio is a good indicator of intelligence, and corvids (crows, as well as ravens and jays) have larger brains than any other bird relative to their body size except parrots. And the
The restaurants, garbage dumpsters, mowed lawns, boulevard trees, wooded parks, engineered ponds and golf courses of suburbia make a sort of Valhalla for many birds.
crow forebrain is organized in clusters rather than layers. This is important because birds belong to a distinct evolutionary line that branched off 300 million years ago. Bird brains and mammalian brains have very different wiring plans and hardware, but their CPUS perform similar tasks. This calls into question the old model of the “tree of evolution,” with human beings at the crown. The “tree” may be more of a shrub, with smart animals developing along any number of off-shooting branches.
For a crow or a human, a large brain has proven to be an asset. Of course, some humans are more intelligent than others. Ditto with crows — in a laboratory, some crows ace tests while others fumble. It’s reasonable to assume that clever crows will do better in a demanding and rapidly changing urban environment. Is it therefore possible that crows are getting smarter?
It sounds like the premise for a spooky movie. But walking through the Burnaby roost, looking up at all those glinting black eyes, it’s impossible not to be captivated by the idea. Crows talk to each other. They build tools and solve problems. They even take transit — in Vancouver, one crow has been filmed riding the Skytrain. The solitary crow gets on the train downtown, minds its own business and gets off in East Vancouver. (It beats flying.) Marzluff says the idea of rapidly evolving super-crows may not be farfetched. “They are definitely changing their behaviour,” he says. “For example, in Japan, when cars stop at a red light, crows will swoop down and place a hard walnut in the path of the tires. Natural selection favours individuals that make good choices, and crows have done so by learning to take advantage of our expanding cities. Crows are evolving culturally — and that is the very definition of evolution.”
Without implying disrespect toward the typical male robin, who might dedicate hours to angrily hurling himself against his own reflection, scientists are learning that crows are smarter than the average bird.