Bear managers and park wardens have tried aversive conditioning before: in Banff, for instance, they used to drive up to bears eating roadside vegetation and blast them with water cannons. But as St. Clair points out, that kind of hazing not only violates several principles of animal learning theory (among them, that punishment should be immediate, consistent and not signaled in advance); all it ultimately teaches a bear is that, through a series of our bylaws, the only humans who will hurt it are humans in uniforms arriving in trucks between the hours of 9 and 5. According to St. Clair, hazing also ignores a breakthrough in animal psychology known as the Garcia Principle (after John Garcia’s work with rats in the 1970s), which suggests that, no matter how hard you try, you may never be able to get an animal to associate food with pain. “It makes complete sense,” St. Clair says. “In terms of its survival, a bear has had no evolutionary reason to associate food with danger.”

But what if every time a bear put its face in the trash, you sneaked up, pulled out a slingshot and hit it in the head with a marble? What if you considered the flipside of the Garcia Principle, which suggests that animals can learn an association between pain and sound (which is why a bear looks up when a tree limb cracks), and five seconds before you whacked that bear with a marble, you blew a whistle in its face? Could you reach deep into its ancient evolutionary machinery and teach the bear that just the sound of a whistle was reason enough to high-tail it out of the trash?

That, at any rate, was the hypothesis, and starting in 2005 Homstol joined with two other young biologists, Nicola Brabyn and Mary von der Porten, to see if they could, as Homstol puts it, “restore normal wary bear behavior” among a group of chronically unwary bears, including a small, swift-footed yearling they took to calling Oscar when he showed up at the transfer station last June.

At 100 pounds, newly on his own, Oscar was having a hard time finding food and avoiding being pushed around by bigger bears. At the transfer station, though, he was getting in and out of Dumpsters with ease, and when Homstol, Brabyn and von der Porten took baseline measurements of his response to humans, Oscar’s score was “indifferent.” When they tried to measure his “displacement distance” — at what distance does a bear run and hide from an approaching human? — they came within 10 yards of Oscar, which is the least amount of space they will put between themselves and any bear, and Oscar didn’t displace; he didn’t even move. “We were wallpaper,” Homstol says.

From the transfer station, Oscar moved into residential neighborhoods, often traveling with other young males. (When food is abundant, Whistler’s bears abandon territoriality and become uncharacteristically social, sometimes even leaving their dens in winter to pick up extra calories.) Together Oscar and one of his companions lingered by condos, trying to remove screens from windows and break into garbage sheds. When a conservation officer darted the other bear to collar him, Oscar remained within steps of the officer, trying to engage his tranquilized companion in play. For five days, from dawn to dusk, Homstol, Brabyn and von der Porten followed Oscar everywhere, and every time they found him in circumstances they deemed “inappropriate” or “conflict,” they pulled out their slingshots and fired at him with marbles. The five-day blitz had some effect: At the sight of an approaching human, Oscar began to move off, sometimes at a “lope,” sometimes even a “run”; and his displacement distance increased to 30 yards. “I felt like Dennis the Menace,” says Homstol, who has a way with a slingshot. “But the thing worked like a charm.”

Following the end of his five-day treatment, Oscar stayed out of trouble for about a week. But soon thereafter, with no more dawn-to-dusk hammering, he was again hanging out in yards and on porches, checking out houses and garages. Once, Homstol got a call regarding a familiar-sounding, small-bodied yearling who had broken into a truck, where he sat in the passenger seat as if waiting for a ride. By the time I was in town, some five weeks later, Homstol was coming to realize that, however effective aversive conditioning might be in the short term, it may simply require too much manpower and probably won’t work on bears that have already progressed down the food-conditioning pathway, especially in communities that can’t secure their waste. “We just can’t keep up,” she said. “Between the C.O.’s and us, there are only six people trying to teach all these bears.” As for Oscar, whatever wariness he learned from five days of marbles seemed to be slipping away without further upkeep, and Homstol concluded that if he stayed in Whistler he’d soon be breaking into houses and end up with a bullet in his chest. She and the town’s conservation officers decided to dart him, put him in a trap and — because he was young, healthy and not the worst offender they’d ever seen — give him a one-way ticket out of town. “Poor Oscar,” she said. “Maybe if we’d gotten to him sooner.”

For several days, Homstol and I went looking for the yearling in her truck. By then, he was a well-known and easily-recognized bear, and driving through town we followed not only his radio signal but also a trail of leads from residents who called in a small bear with collar meeting Oscar’s description. He seemed to be everywhere at once — at this barbecue pit, at that garbage shed — but whenever Homstol arrived at the scene, Oscar had given her the slip.