Researchers continue to monitor bears fitted with GPS collars in northwest Minnesota as part of a study to learn more about the animals in an area that’s on the fringe of their range.
According to Dave Garshelis, bear research biologist for the Department of Natural Resources in Grand Rapids, Minn., the study is tracking nine bears, including six with satellite collars that provide researchers with real-time data.
Two other collars log GPS coordinates, but the information isn’t available until researchers retrieve and download the units. Research crews traditionally change batteries on the collars and download GPS and other data late in the winter while the bears are still hibernating.
A ninth bear has a VHF radio-collar that doesn’t provide latitude and longitude coordinates.
The DNR launched the study in 2007 in partnership with the University of Minnesota and Medtronic, a company that specializes in medical devices and therapies. A key goal of the study, which involved trapping bears and fitting them with the collars, was to get a better handle on the bears’ diets and habitat preferences in northwest Minnesota, which has a mix of brushy and agricultural lands.
Several of the bears also have high-tech heart monitor implants that allow researchers to compare the GPS data with heart rates. If a bear is in a sunflower field or crossing a road, for example, the monitors will correlate whether such potential stress factors result in changes to heart rates. The heart monitors collect data every two minutes.
Older heart monitors used earlier in the study only recorded average heart rates for eight hours during the day and four hours during the night.
“Previously, we would know a bear’s heart rate went up to 200 sometime during the day, but we didn’t know when or what it was related to,” Garshelis said. “Now, we can get it down to, it must have crossed the highway or because it was in someone’s backyard _ something a lot more specific.”
Finding a correlation
Mark Ditmer, a University of Minnesota doctoral student who has been overseeing the fieldwork portion of the project, said the monitors have shown a correlation between heart rates and habitat.
“Bears in crop fields elicit higher-than-expected heart rates, likely due to the stress of foraging in a non-natural area, with human scents and often several other bears in proximity,” Ditmer wrote in an abstract for an upcoming conference of bear researchers.
At the same time, Ditmer said, research has shown larger bears forage on crops such as corn and sunflowers more frequently than smaller bears. The animals with access to calorie-rich crops also conserve energy by traveling less.
During a study of captive bears at the Wildlife Science Center in Forest Lake, Minn., Ditmer said he offered nine bears a menu of field corn, acorns, oil sunflowers and confection sunflowers.
Male bears especially showed a liking for the oil sunflowers followed by acorns, Ditmer said; females initially ate more acorns before warming up to oil sunflowers.
“I believe this shows some form of learning and an insight into risk-aversion,” Ditmer said. “I think males will seek out crop fields wherever they are planted, but females are much less likely to crop raid if the field is not abutting a natural area.”
According to Garshelis, some of the male bears in the study have covered hundreds of square miles. Females tend to travel less, he said, but some of the sows also have covered substantial distances.
“One of the big questions we had was how important are the crops,” Garshelis said. “It seems like a lot of the males focus in on corn or sunflowers during the fall. Some of the females don’t eat crops at all and seem big and healthy. We’re finding hazelnuts are a key part of their diets.”
Garshelis said bears in northwest Minnesota also tend to be larger, on average, than bears in more traditional forested habitat farther east. One collared male east of Middle River, Minn., has tipped the scales at more than 600 pounds, Garshelis said, although researchers couldn’t weigh him this winter.
“He’s out in a swampy area where there weren’t any trees to build a tripod to get him weighed, so we don’t know if he went over 600 pounds again or not,” Garshelis said. “Hunters have seen him and reluctantly passed him up, so that was pretty nice.”
Garshelis said the study didn’t lose any bears to hunters last year.
“We actually sent each hunter a letter and that worked really well,” he said.
Garshelis said there are no plans to trap additional bears. Instead, he said, researchers will monitor the existing bears and continue the study as long as funding allows.
He said the researchers also would like to learn why bears switch to more of a nocturnal feeding pattern in the fall.
There appears to be more to it, he said, than avoiding hunters.
“It occurs right around the time hunters would be putting out bait, but it also occurs in bears where populations are not hunted, outside of Minnesota and in various species of bears and not just black bears,” Garshelis said. “But it always occurs during the fall.”
Minnesota has an estimated bear population of about 18,000, which is below the DNR’s goal of more than 20,000. Garshelis said specific estimates aren’t available for northwest Minnesota.