Mama bears use human shields to protect cubs: study

Male brown bears kill cubs to trigger oestrus—a period of sexual receptivity—in females who would otherwise have come into heat
Male brown bears kill cubs to trigger oestrus—a period of sexual receptivity—in females who would otherwise have come into heat only after raising their cubs to independence

Brown bear mothers in a Swedish forest use human "shields" against murderous males, overcoming their own fear to raise defenceless cubs near villages where hunters live, researchers said Wednesday.

Some young bear mothers have taken to living closer to humans for the duration of the mating season—a period which sends male bears, called boars, into frenzies of lust-fuelled cub killing.

Motherly instinct, in other words, seems to trump sex drive.

While sows grin and bear the potentially threatening proximity for the sake of their offspring, boars continue to give the two-legged species a very wide berth.

"Bears in general avoid areas close to humans," said Sam Steyaert of the Norwegian University of Life Sciences, who co-authored the study in the journal Proceedings of the Royal Society B.

"Also, after the mating season, females with cubs change their behaviour" and go back to avoiding humans, who hunt bears in the forest during a designated season.

Male brown bears kill cubs to trigger oestrus—a period of sexual receptivity—in females who would otherwise have come into heat only after raising their cubs to independence.

This means that instead of having to wait 18-30 months, the males "can obtain a mating opportunity in just a few days," Steyaert told AFP.

The behaviour is called sexually selected infanticide, and has also been observed in birds, bats, primates and big cats.

It is common in brown bears, with as much as a third of cubs in the Swedish forest losing their lives to roving males during the annual mating season, from early May to mid-July.

Steyaert and a team tracked 26 mother using GPS technology between 2005 and 2012.

Of the sows, 16 successfully raised cubs, and 10 failed.

"The median distance of successful females to human habitation was about 780 metres (2,500 feet)," Steyaert told AFP by email.

For unsuccessful ones it was 1,210 metres, nearly half a kilometre farther away.

"Successful mothers were more likely to use humans as protective associates, whereas unsuccessful mothers avoided humans," the study concluded.

Other, less successful strategies, included trying to fight off the aggressors.


Explore further

Increase in bear infanticide linked to hunting

More information: Human shields mediate sexual conflict in a top predator, Proceedings of the Royal Society B, rspb.royalsocietypublishing.or … .1098/rspb.2016.0906

© 2016 AFP

Citation: Mama bears use human shields to protect cubs: study (2016, June 22) retrieved 1 March 2021 from https://phys.org/news/2016-06-mama-human-shields-cubs.html
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