Polar bears sometimes bludgeon walruses to death with rocks and ice, study finds

A new study backs up what Inuit hunters have been saying for centuries: Polar bears use rocks and ice to bludgeon walruses to death. 

For at least 200 years, Inuit in Greenland and Canada have told stories of polar bears grabbing rocks or chunks of ice in their two front paws and lobbing them at the skulls of unsuspecting walruses. Images of the phenomenon have even been documented in Inuit art.

But the scientific community has largely ignored these tales, or dismissed them as hearsay and myth — until now.

“One of the things that I have done over the years is worked with a lot of experienced Inuit hunters out on the sea ice, and one thing that you become aware of very quickly is that if an experienced hunter tells you he’s seen something or describes something, you can pretty well take that for granted that that’s quite true,” Ian Stirling, a polar bear expert from the University of Alberta, told As It Happens guest host Ginella Massa.

“So the fact that there were so many of these kinds of reports, and they were all really quite basically similar, indicated that there was something out there that might be worth looking at.”

Stirling and his colleagues pored through decades worth of documented traditional Inuit knowledge, including a report from an Inuit hunter in the mid-’90s, as well as recent evidence of a bear in captivity using tools to access its food. They concluded that this is a rare — but very real — behaviour. 

Their findings are published this past June in the Journal of the Arctic Institute of North America

Ian Stirling is a scientist emeritus for Environment and Climate Change Canada and an adjunct professor in the Department of Biological Sciences at the University of Alberta in Edmonton. (Ian Stirling)

Stirling — a research scientist emeritus for Environment and Climate Change Canada and adjunct professor in the U of A’s Department of Biological Sciences — is one of the world’s foremost polar bear experts, and says he’s always been intrigued by their intelligence.

So his interest was piqued when he heard about GoGo, a male polar bear at a zoo in Japan that showed a propensity for using tools — a skillscientists have long held up as a major signifier of of intelligence in animals. 

GoGo’s keepers hung meat above his enclosure, out of the bear’s reach. But the clever creature devised several methods for getting his grub — either knocking it down with a stick, or grabbing a large object and “shooting it with both paws like a basketball player” toward the food, Stirling said.

The latter is the same technique the animals use to kill walruses, according to Inuit accounts. 

“The most significant part of this is that a bear is able to look at a situation, think of it in a three-dimensional sense, and then figure out what it might have to do to be successful,” Stirling said.

In other words, bears are problem solvers. And in this case, the problem that needs solving is the walrus’s big, thick skull.

“They normally hunt seals, and the seals have skulls which are very easy to crush when the polar bears bite,” Stirling said.

“But walruses have very heavy, thick skulls and a polar bear simply cannot bite into the skull and kill the animal by doing that.”

So instead, a bear may grab a rock or a chunk of ice and lob it at the walrus, either killing it outright, or stunning it so it can come in close and finish the job. 

GoGo, a male polar bear in Tennoji Zoological Gardens, Osaka, Japan, uses tools to fetch food that’s out of his reach. (Tennoji Zoological Gardens/Journal of the Arctic Institute of North America)

Gabriel Nirlungayuk, an Inuk hunter of Rankin Inlet in Nunavut, told ScienceNews.org that he hasn’t personally witnessed a polar bear using tools to hunt walruses, but he’s heard stories.

“I’ve seen polar bears since I was probably seven years old. I’ve been around them, I’ve hunted alongside them, and I have seen their behaviours. The smartest hunters are usually the female bears,” he said, noting that some polar bears will trick seals into getting close by pretending to be asleep.

“I have worked with the Inuit on traditional knowledge for a very long time and one of my favourite subjects is polar bears, because science often suggests one thing and the Inuit say another thing,” Nirlungayuk said.

Stirling says scientists don’t know whether the bears figure out themselves how to use hunting tools, like GoGo apparently did, or whether they teach the technique to each other, like cockatoos opening garbage bins, or dolphins using seashells to catch fish.

“It seems most likely to me that adult polar bears that pick it up are figuring it out by themselves independently,” he said.

“That said, if it’s figured out by a female bear and she’s accompanied by her cubs, and the cubs see what she’s doing, they’re very likely to remember it and will try to apply it in the right circumstance in time.”

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