Ongoing study shows how black bears thrive on agricultural landscapes
By Shelly Gustafson
Looking out over the primarily agricultural landscape in northwestern Minnesota, the last thing one would expect to see is a black bear snacking on sunflowers and corn. But that is exactly what a group of researchers, including recent CFANS graduate and Ph.D. recipient Mark Ditmer, discovered in a recent study that focused on explaining the growing population of black bears in this unlikely habitat.
Launched in 2007 as a joint research project between the Minnesota Department of Natural Resources (DNR), the university and Medtronic Inc., the research initially focused on understanding the limitations of bear range and what is needed for black bears to not only survive but thrive in habitats like northwest Minnesota, says Dave Garshelis ('83–Ph.D., Wildlife), the DNR's black bear biologist and an adjunct associate professor for the Department of Fisheries, Wildlife and Conservation Biology.
In 2009 Garshelis's team needed a new graduate student to assist with the project and Ditmer, newly arrived at the U, needed a research project he could sink his teeth into. Ditmer had discovered his interest in conservation biology while doing renewable energy consulting in Washington, D.C., and was interested in discovering more about the bears' behavior and how it related back to their diet, home range and overall health.
Early research showed that the bear population was not only growing in northwest Minnesota, but the bears were thriving in the area. Significantly, the team found the bears were among the biggest and most fecund in the state. The question remained, however, if the area would be able to continue to sustain the growing population.
To help answer this question, the research team fit the bears with GPS collars, which recorded their movements and showed that the bears have a much larger home range than any other black bear population. While it is common for a bear's home range to expand and contract as different food sources become available, large home ranges generally mean a habitat is lacking in significant food resources, says Ditmer. In contrast, in northwest Minnesota it appears to derive from the wide spacing of food, found in small patches of forest, as well as scattered fields of corn and sunflowers; these edible crops comprise only 2 percent of the landscape.
"We were able to see that even if the crops went away, we think the area is still pretty suitable for bears because there are a lot of younger forests and there is a lot of natural food available," says Ditmer.
Beyond their eating habits and size, Ditmer was interested in learning more about the bears' behavior. To do this he combined information from the GPS collars with information from Medtronic's cardiac biologgers implanted under the bears' skin. A correlation soon came to light as Ditmer noted that the bears' heart rate increased sharply when they are involved in stressful behavior, such as crossing roads or open farmland.
"When bears are crossing agricultural areas that are wide open, their heart rate does spike more than you would expect given their rate of movement," says Ditmer. "In contrast, when they find the crops they like to eat, their heart rate becomes very slow, indicating not only that they are immobile but also unstressed."
Also surprising, they found that mainly the males were bold enough to help themselves to the nearby crops. Females, especially those with cubs, tended to avoid large males reigning over small cornfields and found plentiful acorns and hazelnuts in the woodlots.
The team's research has looked not only at the effect of this unusual landscape on the bears, but also has taken into account how the bears have affected farmers in northwest Minnesota. While a few are finding their new neighbors a nuisance, for the most part Garshelis says that many either don't realize or don't care that the bears are causing the crop damage. Deer are still the primary crop nuisance in the area, and a few thousand oversized bears have not changed that.
Moving forward, Garshelis will continue to partner with Medtronic and university researchers to study this ever-growing bear population. A new generation of heart rate monitors will allow them to receive more detailed information. Ditmer will be exploring his love of animals and conservation in new research areas but plans to keep up with the project and possibly assist in the field.
"Mark has been a pleasure to work with," says Garshelis. "He has an analytical mind and took the data well beyond anything we imagined."