Is Aspen a 'sink' or source for bears?
Graduate study focuses on how area population is faring
Janet UrquhartA five-year study of black bears in the Aspen area wrapped up this month with the retrieval of GPS collars from hibernating sows and the collection of data that may yield new information about urban bear populations. The Roaring Fork Urban Bear Ecology Study had been tracking scores of bruins in the Aspen area since 2005. Bears were fitted with collars in order to track their movements and analyze their travel patterns. The last of those collars was to be collected on Thursday in the Difficult Creek area, east of Aspen. The devices are headed to Durango for a bear population study there, and Aspen's bears will go back to wandering the woods in relative anonymity, assuming they don't get into trouble in town.
Colorado State University graduate student David Lewis, who has been leading ski excursions into the backcountry around Aspen of late to retrieve the collars, has more than the tracking devices on his mind, however, when he locates another den where a slumbering sow has holed up for the winter. He's tallying the young bears in the den, or noting the lack of offspring, for his own master's thesis. Lewis wants to know if Aspen's bear population is on the increase, or dropping, given a multitude of variables that can affect that number. He expects to wrap up his thesis in May 2012. "We're trying to find out if Aspen is a source for the bear population or a sink for the bear population," he said. "Aspen should be a source, because it has such good habitat, but it may be a sink because of the euthanizations — because of conflicts.
"The whole question is, how is an urban environment affecting a regional bear population?" he said.
The number of bears euthanized by state wildlife officers in Pitkin County dropped from 20 in 2009 to two in 2010, according to the Colorado Division of Wildlife. Plentiful food in the backcountry last year was credited for keeping bears out of towns, and out of trouble. Lewis hopes to determine whether the population is able to hold its own over time — if enough cubs are born, and survive, to maintain a thriving bear population despite the bears that are lost to hunters or put down by wildlife officers.
Lewis visited seven dens this spring — two in January and five in March. Before Thursday's scheduled outing, he had tallied one sow with three cubs, two sows who each had two cubs in the den, and one young sow with one cub. Years with an abundant natural food supply for bears, as last year was, should mean a spike in the birth rate, but even when the food supply is lacking — years when sows shouldn't produce offspring — they continue to do so, according to Lewis. The food bears find in town apparently makes up for natural sources, Lewis said.
Nonetheless, Lewis said he suspects Aspen is a bear "sink" — that the population is on decline as a result of factors like human-bear conflicts that lead to bear deaths.
In some years, dozens of bears are also trapped and relocated away from Aspen — 33 were taken elsewhere in 2009. Those bears are not necessarily gone, though, according to Lewis. Bears have wandered back to the Aspen area from as far away as Meeker and Colorado Springs, he said. One bear trapped locally was released in the Salida area and from there roamed to Colorado Springs and then back toward Aspen. It was shot by a hunter on Basalt Mountain, Lewis said.
The original study, tracking bear movements, indicated bears don't get addicted to human food sources, but will remain in the wilds when natural food, like berries and acorns, is plentiful. Sharon Baruch-Mordo, a doctoral candidate at Colorado State University, reported those findings last summer. She led the study, a joint venture between CSU, the U.S. Department of Agriculture and the DOW.--a contradiction as apparently human food does embolden bears to get in close to human settlements and end up on the dead end of a rifle--blogger Rick
In all, 62 bears were collared during the five-year study, according to Lewis. Though they are no longer collared and tracked (except for the two or three bears Lewis hasn't been able to locate), each has an implanted tag containing information that can be scanned if the animal is captured.
Colorado State University graduate student David Lewis, who has been leading ski excursions into the backcountry around Aspen of late to retrieve the collars, has more than the tracking devices on his mind, however, when he locates another den where a slumbering sow has holed up for the winter. He's tallying the young bears in the den, or noting the lack of offspring, for his own master's thesis. Lewis wants to know if Aspen's bear population is on the increase, or dropping, given a multitude of variables that can affect that number. He expects to wrap up his thesis in May 2012. "We're trying to find out if Aspen is a source for the bear population or a sink for the bear population," he said. "Aspen should be a source, because it has such good habitat, but it may be a sink because of the euthanizations — because of conflicts.
"The whole question is, how is an urban environment affecting a regional bear population?" he said.
The number of bears euthanized by state wildlife officers in Pitkin County dropped from 20 in 2009 to two in 2010, according to the Colorado Division of Wildlife. Plentiful food in the backcountry last year was credited for keeping bears out of towns, and out of trouble. Lewis hopes to determine whether the population is able to hold its own over time — if enough cubs are born, and survive, to maintain a thriving bear population despite the bears that are lost to hunters or put down by wildlife officers.
Lewis visited seven dens this spring — two in January and five in March. Before Thursday's scheduled outing, he had tallied one sow with three cubs, two sows who each had two cubs in the den, and one young sow with one cub. Years with an abundant natural food supply for bears, as last year was, should mean a spike in the birth rate, but even when the food supply is lacking — years when sows shouldn't produce offspring — they continue to do so, according to Lewis. The food bears find in town apparently makes up for natural sources, Lewis said.
Nonetheless, Lewis said he suspects Aspen is a bear "sink" — that the population is on decline as a result of factors like human-bear conflicts that lead to bear deaths.
In some years, dozens of bears are also trapped and relocated away from Aspen — 33 were taken elsewhere in 2009. Those bears are not necessarily gone, though, according to Lewis. Bears have wandered back to the Aspen area from as far away as Meeker and Colorado Springs, he said. One bear trapped locally was released in the Salida area and from there roamed to Colorado Springs and then back toward Aspen. It was shot by a hunter on Basalt Mountain, Lewis said.
The original study, tracking bear movements, indicated bears don't get addicted to human food sources, but will remain in the wilds when natural food, like berries and acorns, is plentiful. Sharon Baruch-Mordo, a doctoral candidate at Colorado State University, reported those findings last summer. She led the study, a joint venture between CSU, the U.S. Department of Agriculture and the DOW.--a contradiction as apparently human food does embolden bears to get in close to human settlements and end up on the dead end of a rifle--blogger Rick
In all, 62 bears were collared during the five-year study, according to Lewis. Though they are no longer collared and tracked (except for the two or three bears Lewis hasn't been able to locate), each has an implanted tag containing information that can be scanned if the animal is captured.
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