There was a far more serious reason that polar bears ate so much caribou

Image: BROADALLY TRADED PRODUCTS A polar bear was supposed to have acquired its abnormal eating pattern because it harvested caribou. But a new study published in PeerJ shows another hunter actually caused the polar…

There was a far more serious reason that polar bears ate so much caribou

Image: BROADALLY TRADED PRODUCTS

A polar bear was supposed to have acquired its abnormal eating pattern because it harvested caribou. But a new study published in PeerJ shows another hunter actually caused the polar bear’s feeding habits to change – the same same hunter who spent time with a pygmy eider.

Polar bears have a huge diet – from seals to seals to seals, but they also spend some time catching caribou. Some polar bears are more voracious eaters than others, and that can make a big difference to their dietary needs. But there’s been debate for years about what exactly makes polar bears put on the pounds.

A new study in PeerJ, led by Daniela Di Re and Marcin Tomek of the Italian Polar Research Institute, reveals that a polar bear near Trumalokuk in Canada’s Hudson Bay found itself out of position on this giant antler of a caribou a short while after eating a few pounds of the meat of a “highly favoured” eider. And that voracious eider wasn’t blubber, but rather “alternative food sources” as Di Re calls them – different kinds of food that aren’t part of their current normal diet.

The study sheds new light on the way polar bears acquired this kind of voracious eating habits, Di Re told me over email. And those findings could explain how polar bears gained the weight they lost in earlier years, resulting in the spike in mortality rates from 2007 to 2010, when there were 473 deaths and 280 missing polar bears from the Hudson Bay region.

“In this way,” Di Re said, “the energy influx from prey, gained with different kinds of other food sources, could be transferred to the body without the loss of weight, and in fact, give a similar nutritional status of the body.”

Di Re said she’s not sure whether polar bears’ voracious eating habits are simply an adaptation for increased energy from food sources, like seals, that they don’t eat today. But she suspects that this voracious-eating behaviour developed independently of a range of other feeding behavioural traits.

“I am convinced that “alternative eating habits” must be the primary (hormonal) or only contributing (chemical) reason for the increase in the weight of the polar bear in the Hudson Bay region from 1960 to 2010 and the disappearance of the polar bear,” Di Re said. “Many other features, such as “hunting skill”, “ambition” or “feathering” are the key parameters of the polar bear’s energy intake, which act in a compartmentalised fashion.”

The study’s main finding is just one example of the way a hunter has a big impact on a predator’s food intake, though it doesn’t explain every eating preference that other species have, according to John Fielkow, a virologist at Southern Illinois University who wasn’t involved in the study. Still, Fielkow says he’d have more questions about Di Re’s conclusions if it weren’t for the fact that the results are limited to one population of polar bears.

“This study is very much in line with what other studies have found, such as that bovine goats enter the stomachs of ground-running prey that are as food-nosed as dogs – especially if they are ritually slain before they devour the prey,” Fielkow told me in an email. “It is this finding, and not some ‘less lethal method’ of devouring certain animals that makes this particular animal [fish or rabbit] more susceptible to stomach vorality than other mammals.”

What the study does show, Fielkow said, is the importance of understanding how hunter-gatherers get the kind of food that a predator is eating. It’s important, he said, to “question our assumptions when it comes to nutrition, nutritional behaviour, and feeding species.”

[PeerJ]

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