Black bears (Ursus americanus) have efficiently adapted to the urban couch potato lifestyle, according to a recent study that compared urban and wild land bears in the Lake Tahoe region of Nevada.

Given a readily available and replenishing food resource—garbage dumpsters—the urban bears are nearly a third less active and weigh up to thirty percent more than bears living in more wild areas, biologists with the New York-based Wildlife Conservation Society report.

"A lot of people suggested [bears] might alter their behavior in the presence of humans. We went out and specifically tested some of these hypotheses with rigorous science," said Jon Beckmann, a biologist with the society's Eastern Idaho Field Office in Rigby.

Beckmann and colleague Joel Berger report their findings in the current issue of the Journal of Zoology. The Wildlife Conservation Society biologists were at the University of Nevada, Reno, when they conducted the research for the study.

In addition to seeking grub in dumpsters behind fast-food joints and suburban neighborhoods instead of foraging for wild berries and deer in the mountains, urban bears have also become night owls, whereas wild land bears are active during the day.

Mike Mitchell, a U.S. Geological Survey bear researcher who teaches at the School of Forestry and Wildlife Sciences at Auburn University in Alabama, said the findings are pretty much what he would expect.

"Bears are extremely efficient foragers and so intelligent, resourceful, and adaptable," he said. "They'll figure out a good food resource almost instantly and make the best use of it as quickly as they can."

Mitchell added that urban bears are not lazier than wild land bears, just more efficient. Since they live in a garbage-can-rich environment, they expend less energy than do bears that have to forage in untamed lands for hours to get the same caloric intake.

Wild Land Impact?

Beckmann and Berger present evidence in their study that more and more bears are relocating to the cities, leaving wild lands sparsely populated by the big, furry carnivores. They question what impact this change in behavior is having on the environment.

"It's possible that if we change their behavior, we can lose the ecological processes they are involved in," said Beckmann. "For example, bears that now have a reliance on garbage may not be doing the things bears have historically done in those systems."

While the ecological role of bears is poorly understood, biologists believe they may be important in decomposing felled logs, dispersing seeds of berries, and removing rotting flesh from the forest floor.

Mitchell said that he is not certain of the extent to which non-urban bears are moving to the cities, and if they are what sort of an effect the re-location would have on the untamed environment.

"In principle, one has to believe that an effect exists, but defining that effect clearly and quantifying its magnitude might be very difficult to do," he said.

Bear-Proof Garbage

Regardless of the impact an exodus of bears from the wild lands to the cities might have on the environment, the researchers all agree that a population of bears relying on food from garbage cans is not a healthy situation.

There is no evidence to suggest that the garbage itself is a bad diet—though Beckmann said he can't imagine it's good, either—but the increase in urban bear populations has resulted in an increase in bear mortality, primarily from collisions with vehicles.

The dumpster-diving bears are also quick to learn where the food in the garbage cans comes from, and incidents of bears breaking into cars and homes when people are asleep are on the rise.

"Such conflicts rarely work out well for the bears," said Mitchell. "It is hard to imagine the development of a stable, commensal relationship between high density populations of bears and people."

As a remedy to the problem, Beckmann and Berger suggest that city planners and county commissioners require individuals and businesses to purchase and use bear-proof dumpsters.

"We know they work," said Beckmann. "Once they go into a homeowners association, the bears no longer visit."