Mama bear knows best.
Between May and July each year, brown bear cubs live in constant danger. The mating season brings about violent tendencies in adult males, who regularly kill cubs to trigger sexual receptivity in mothers who would otherwise come into heat only after raising their cubs to independence.
But mama bears, notoriously protective of their cubs, have acquired protection from an unexpected source — human hunters.
Over a 7-year period, researchers monitoring brown bears in a Swedish forest using GPS technology observed 19 instances of mothers successfully raising their cubs, while 11 litters were lost to infanticidal males.
The researchers noticed that some mothers had taken to living near villages where hunters reside for the duration of the mating season. This choice of habitat was highly unusual, as bears generally avoid areas close to humans.
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When the mating season ended, those mothers shifted back to their usual human-avoidance behavior.
But their temporary change of location paid off. Those that had ventured closer to human-occupied territory were more likely to have surviving cubs.
“They were clearly using the humans as a shield,” Sam Steyaert of the Norwegian University of Life Sciences, who co-authored the study in the journal Proceedings of the Royal Society B, told Science Magazine.
The median distance of successful females to human habitation during the mating season was 783 meters. “These mothers select the densest vegetation, especially when they’re close to humans,” Steyaert said. “That way they can be very close to people, but the people don’t know they’re there.”
Unsuccessful females maintained a cautious distance of nearly half a kilometer farther away from humans, but in doing so, gave their cubs greater exposure to potentially infanticidal male bears.
According to the researchers, this study shows that “female bears can increase their reproductive success by using human footprint as a shield against infanticide.”
Similar protective associations have also been documented in moose in living in Yellowstone, that give birth near roads to keep predatory traffic-averse brown bears away from their offspring, and mountain nyala in Ethiopia that use human shields against their spotted hyena predators.
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