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Bears: Handle With Care

21 August 2008 (All day)
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Foothills Research Institute/Grizzly Bear Research Program

Secretly stressed. Bears show deleterious effects from being captured and handled.

Like physicians, wildlife biologists first want to cause no harm to the animals they study. But an analysis of the long-term effects of capturing and handling two species of bears--grizzly (Ursus arctos horribilis) and American black (Ursus americanus)--indicates that the animals suffer more than previously thought. "We're throwing up a red flag," says Roger Powell, a wildlife biologist at North Carolina State University in Raleigh and one of the study's authors. Powell suspects that the results apply to any species that is handled. "It's time to step back and reevaluate our methods."

Powell's colleague, Marc Cattet, a wildlife biologist at the University of Saskatchewan in Canada, began suspecting problems in the wildlife he was capturing about 5 years ago, particularly among grizzly bears in the Canadian Rocky Mountains. "Basically, their muscles were sore, and consequently, they roamed around their territory less," he says. When Cattet raised his concerns with other biologists, most suggested that there was something wrong with his handling methods. But most did not have the necessary data to do similar evaluations on their animals. Powell did.

"I had 22 years of data on black bears" from a study site in North Carolina, says Powell, who adds that he'd never noticed a problem until Cattet suggested he take another look. "And son-of-a-gun, I found the same thing"--a 2-week decrease in the bears' movement around their territories. "Then they increased their movements for another 2 weeks, as if they were making up for lost time," before settling back to normal.

Bears go through a lot when being studied. When Powell, Cattet, and other biologists need information on the health of a bear population or its roaming habits, they have to capture a few animals. That means leg-hold snares, barrel traps, or helicopter darting. Once the bears are subdued, the researchers may anesthetize them, weigh and measure them, and extract teeth, blood, and tissue. They may also fit them with radio collars. All are standard and approved methods for handling wildlife.

To see just what kind of impact this has on bears, Cattet, Powell, and colleagues reviewed their combined data from 32 years of bear capture--analyzing blood samples from a total of 340 black and grizzly bears. The study, published in this month's issue of the Journal of Mammalogy, found that six of every 10 captured bears had abnormally high values for muscle enzymes, an indication of muscle injury probably caused by stress and exertion as the bears tried to escape. The team also found that bears captured multiple times lost body fat or did not gain body fat at the normal rate. Because body fat is important for growth and reproduction, this finding is particularly worrisome, says Cattet. What's more, the effects of capture could lead to erroneous interpretations about the bears' true behaviors, the team says.

"This is a significant addition to the debate on the impacts of wildlife capture," says Samuel Wasser, a conservation geneticist at the University of Washington, Seattle, who has developed noninvasive techniques for studying the health of wild animals, including analyzing feces. "It's increasingly difficult to justify" using invasive methods, he adds. "The study is an eye opener," adds William Zielinski, a research ecologist with the U.S. Forest Service in Arcata, California, who has handled numerous species of wild animals. "It's an impetus to all of us to evaluate our work, to use less-invasive methods, and not to capture animals unless absolutely necessary."