Northwest Minnesota bear study digs into detailsIt’s too early to draw conclusions, but preliminary evidence suggests bears could establish populations farther south and west in Minnesota than researchers initially thought.
By: Brad Dokken, Grand Forks Herald
A high-tech study of black bears in northwest Minnesota eventually could shed light on how far the species can expand from its traditional northern forest range.
It’s too early to draw conclusions, but preliminary evidence suggests bears could establish populations farther south and west in Minnesota than researchers initially thought.
“I think it’s going to be quite surprising how far they can go,” said Dave Garshelis, bear research biologist for the Department of Natural Resources in Grand Rapids, Minn. “How humans respond to them in areas with little forest and more reliance on crops will probably be the limiting factor.
“I don’t think they’ll quite make it to North Dakota.”
As part of a study with collaborators from the University of Minnesota and Medtronic, the DNR since 2007 has been fitting bears in northwest Minnesota with GPS collars to learn more about their movements and habitat use in a part of the state that’s on the fringe of bear range.
The number of bears with collars has varied, but 11 bruins now have the GPS units. Medtronic and a surgical lab at the U of M, which helped fund the collars, also implanted heart monitors in some of the bears.
According to Garshelis, six of the GPS collars transmit location data to a satellite, and he and other project researchers get daily email updates. The remaining collars simply store information until they can be removed and downloaded.
Garshelis said the study’s main focus has been to look at how bears in northwest Minnesota live in fragmented habitat with relatively small woodlands, and how they subsist in agricultural areas that don’t provide food until late summer when crops mature.
Through a scientific process called “stable isotope analysis,” researchers by examining hair samples can tell whether the bears are relying on crops or natural foods for the bulk of their nutrition. Furthermore, information from the heart monitors can be correlated with the GPS data to estimate how much energy the bears are expending to obtain that nutrition.
“What are the advantages energetically from feeding in a corn or sunflower field?” Garshelis said. “We hope to make predictions on an energetic basis on how far west or south bears can expand.
“This is one of the few places in the country where sunflowers are a big part of bears’ diets.”
The study, to date, has shown that male bears in the northwest rely on crops, primarily corn and sunflowers, for nutrition more than female bears. They also travel longer distances, Garshelis said, in some cases 20 to 30 miles a day.
That’s especially true in the fall as they fatten up for winter.
In an effort to determine why male bears are more dependent on crops, researchers last fall conducted a series of tests with captive bears. According to Garshelis, the bears were given dishes with acorns, corn and both oil and confection sunflowers to see which foods they preferred.
“The males right away would dive into the oil sunflowers, and the females always started with the acorns,” Garshelis said. “Eventually, they would learn the oil sunflowers were pretty good and provided a lot of calories, but it would take about three trials before they discovered this.”
Mark Ditmer, a doctoral student in the U of M’s conservation biology program, is analyzing the data for his dissertation. According to Garshelis, that includes all of the GPS, heart data, hair samples and captive feeding trials — analysis that has never before been done on bears.
Based on the tests, Garshelis said, it appears female bears haven’t fully caught on to crops as a good food source. Males also are bolder, which could explain why they travel longer distances for food.
“I think they’re just more inclined to look for places that have a big abundance of food, places with lots of acorns or corn or sunflowers where they can put on a lot of weight very quickly,” Garshelis said. “Females are more inclined to make do with the foods they have in their normal home range, which is a less risk-averse strategy.”
Garshelis said the researchers this past winter tracked a bear to a site west of Red Lake Falls, Minn., which is the farthest west they had documented a den in the study. When they got to the den, they found the bear dead and frozen.
Data from the heart monitor showed the bear had died near the end of hunting season, suggesting it could have been shot.
Bears also have been lost to vehicle kills, shot as nuisance animals, and one bear was taken during the spring season in Manitoba. In other cases, researchers simply lost contact with bears.
“It just goes to show you how difficult it is to keep a study going,” Garshelis said.
As the study winds down, Garshelis said there are no plans to collar additional bears this summer, although he hopes to recapture a male bear this week near Plummer, Minn., to download the data from a collar that seems to be malfunctioning.
Plans also are in the works to set up a website for the public to track the six bears with the satellite collars in real-time. That should be online within the next month or so, Garshelis said, but will be taken down or delayed during hunting season.
Minnesota has an estimated population of about 18,000 black bears, but the northwest is the only part of the state where the population is growing, Garshelis said.
Northwest bears also are bigger than your average bear in Minnesota. They might live on the fringe of bear range, but they’re doing well, Garshelis said.
“They seem to be a lot bigger” in the northwest, he said. “The dead center of bear range is right here in Grand Rapids, so we have a lot of information on weight of bears. If you do a side-by-side comparison of the males and females of specific ages, you can see the growth rate of the bears in the northwest is quite a bit faster. An average one-year-old in the core of bear range might be 45 pounds, and it will be about 75 pounds in the northwest.”
Dokken reports on outdoors. Reach him at (701) 780-1148; (800) 477-6572, ext. 148; or send email to firstname.lastname@example.org.