Humans Are Changing The Way Mama Bears Raise Their Young

Scandinavian brown bear mothers are holding on to their cubs longer than ever before, and it’s not just because they’re adorably fluffy and cuddly. Turns out, it’s an adapted strategy that could also be a major survival advantage, and it may be caused by humans.

As in many other countries, it is illegal in Sweden to kill a mother bear who has a cub. Now, researchers suggest these brown bears are adapting to human hunting behaviors by staying with their cubs longer.

“Generally, the cubs have followed their mother for a year and a half,” said Professor Jon Swenson from the Norwegian University of Life Sciences (NMBU) in a statement. “Only rarely have we observed them follow her for two and a half years.”

Now, it looks like that 2.5-year timeframe is on its way to being the norm. Between 1987 and 2015, scientists followed 164 litters from 62 different females. Since 1993, almost 25 percent of cubs are staying with mum for that extra year. During the hunting season, female brown bears with young have a survival advantage over those who don’t. The longer females are with their cubs, the more time they avoid being killed – the odds of being killed is almost four times higher for solitary females, compared to adult females with cubs.

Human behavior, in the form of hunting, may be affecting the way Scandinavian brown bears reproduce too. “Man is now an evolutionary force in the lives of the bears,” said Swenson.

If mums are spending more time with their cubs then they have less time to reproduce, reducing the overall amount of offspring they will have throughout their lives. “In an evolutionary perspective, this would not be beneficial,” said Swenson. “The animals with the most offspring “win” nature’s race.”

But the research shows the increased life expectancy found in females counteracts the reduced birth rate. If this behavior is passed down to other generations, researchers say it could lead to an evolution within the population.

Published in Nature Communications, the study was done in conjunction with the Scandinavian Brown Bear Project. Since 1984, the project has been following brown bears and is one of the world’s two largest research projects on bears, according to Swenson, who has been with the program nearly as long as it’s been around.

“We have followed over five hundred bears, many from birth to death,” he said.

During this time, the number of hunted bears in Sweden has increased steadily. Between 2010 and 2014, scientists say hunters shot about 300 bears annually.

Brown bears first arrived in Sweden after the last Ice Age, about 10,000-14,000 years ago. Although population numbers currently are around 2,800-3,000, the Swedish government reintroduced hunting in 2010 to keep the numbers under control. In 2015, the Swedish Species Information Centre re-listed the bears as “threatened” on its Red List, mainly due to hunting.


Leave a Reply