In parts of Alaska where brown bears (Ursus arctos) prey heavily upon the calves of caribou (Rangifer tarandus) and moose (Alces alces), fastening collar-mounted cameras on the bears could be an effective way to track how many calves they’re killing.
These cameras may be more accurate than other techniques biologists use to detect an individual’s kills, said Christopher Brockman, a wildlife biologist with the Alaska Department of Fish and Game and lead author on the paper, which was published in the March issue of The Wildlife Society Bulletin.
“Kill rates were three to four times higher than anything that had been previously measured for ungulate calves,” Brockman said.
By examining moose populations there, the biologists had observed that bears were killing a high proportion of calves. That led them to try to quantify individual bears’ predatory behavior. As an offshoot of a broader bear monitoring project, Brockman and his colleagues fit 17 of the animals in south-central Alaska’s Nalchina Basin with camera collars over a three-year study. From 2011 to 2013, for about six week after calving began each May, they recorded the bears’ activity for 10 seconds every 10 minutes.
Previously scientists had tried to quantify calf kills by collaring newborn moose, investigating kill sites when the collars indicated calves had died and determining what predator species was responsible. But this method didn’t reveal which individual had done the killing, Brockman said, and it excluded calves without collars.
Researchers had also tracked bears after attaching radio or GPS collars on them. But watching and sampling these large carnivores’ predatory activity over their vast habitat for a sufficiently representative period of time isn’t easy, Brockman said.
“They can process a calf in a short time, so methods previously used weren’t monitoring at frequent enough intervals to detect a good portion of kills,” he said.
An earlier study applied camera collars to caribou.
“The technology is promising,” Brockman said, although it’s still limited by the cameras’ memory and battery capacity.
“If we can use this in the future and those kill rates we measured are applicable for the whole population, it’ll help managers in refining their models of how populations of predators and prey in this area fit together, how harvesting bears may increase ungulate populations and allow for increased harvest,” he said.
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