Mother bears in the wild are using humans as bodyguards to protect their cubs, according to new research.
The findings, published in the journal Science Advances, add to the growing body of evidence that people can sometimes unwittingly help to shield certain wild animals from being killed.
Earlier research has found that mother moose in Yellowstone National Park preferentially shift their calving grounds near people to help prevent their offspring from being attacked by traffic-averse predators. Mountain nyala, a type of antelope, also appear to intentionally settle near humans in Ethiopia to help prevent hyena attacks.
As for bears, some clever moms seem to have figured out that humans help to safeguard against infanticide, where an adult male bear kills cubs that he has not fathered in order to free the female to mate with him. Researchers strongly suspect that Scandinavian brown bear (Ursus arctos) mothers fear dominant males of their own kind more than they do humans.
Lead author Sam Steyaert explained to Discovery News why infanticide might have evolved in this species.
“Maternal care in brown bears can last very long; the cubs stay up to two years with their mothers, and up to 3.5 years in some other populations,” he said. “During this period of maternal care, the mothers don’t mate, but once they separate (from their cubs), the females mate again.”
Steyaert, a researcher at the Norwegian University of Life Sciences and the University College of Southeast Norway, senior author Andreas Zedrosser and colleagues have been studying this species of bear as part of the Scandinavian Brown Bear Research Project.
For this latest study, they tracked the bears within a managed boreal forest in south-central Sweden that is intersected by a dense network of roads and that includes some human settlements at various points. The researchers found that many mother bears with cubs were choosing to settle closer to more populated areas. Those mothers that did so greatly increased their litter’s chances of survival.
As the researchers wrote, “Successful mothers were more likely to use humans as protective associates, whereas unsuccessful mothers avoided humans.”
Steyaert said that he and his team aren’t sure how this all developed.
“It might be a learned strategy or an individual tactic,” he said. “There is a lot of individual variation in behavior in bears, and personality may play a big role in there.”
Nearly all bears fear humans to some degree, and for good reason. Hunting bears in the Swedish wilderness is popular. So mother bears and their cubs settle in areas that are close, but usually not too close, to humans.
“The median distance from human habitation for successful mothers was about 700 meters (.4 miles), so it is not that these mothers are in the backyards of people all of the time, but they are in relative close proximity,” Steyaert said.
The new findings could help explain why so many unexpected human encounters with bears in North America, Europe and Asia involve mothers and their cubs.
Marcus Elfström, a biologist at the Sweden-based organization EnviroPlanning, told Discovery News that the study “provides evidence that female bears can increase their reproductive success by using human footprint as a shield against infanticide.”
Elfström said that the most accepted explanation is that bears associate people with easily accessible food. Earlier studies from the Scandinavian Brown Bear Research Project, however, have found that the physical condition of bears close to settlements vs. bears that were in more remote regions were basically the same.
“These (earlier) results give little support for food search or food shortage to explain the occurrence of problem brown bears near settlements in Europe,” he said.
Habituating to people and their wasted food might occur after the mother bears settle near humans with their cubs, not beforehand.
“Attractant management is important,” Elfström said, “but failure to consider interactions among bears may lead to only treating the symptoms of habituation or conditioning. Bears seeking refuge near settlements may not be viewed as ‘unnatural,’ but rather as an example of an adaptive behavior to avoid dominant (male bears), which use habitats farther from people.”
Bears can enjoy more than one benefit from living near humans, but do people — and specifically non-hunters — who have bears living nearby experience any gains, too?
Steyaert thought for a minute and then said, “Benefits for humans? A larger chance to observe a bear.”