Polar bears sometimes use stones and ice to hunt walruses, study finds

Posted on : 2021-09-05 10:36 KST Modified on : 2021-09-05 10:36 KST
A team of researchers from Canada, the US and Greenland concluded that it was rare but possible for polar bears to use tools when hunting walruses
An engraving of a polar bear hurling a rock at a walrus from Charles Francis Hall's 1865 book Arctic researches and life among the Esquimaux.
An engraving of a polar bear hurling a rock at a walrus from Charles Francis Hall's 1865 book Arctic researches and life among the Esquimaux.

Stories of polar bears using clever methods to hunt walruses are widely shared among Inuit hunters.

It would be suicidal for the bear to simply charge at the walrus, which is three times its size and has huge, threatening tusks. Instead, the bear will climb up to a high location near where a walrus is resting and kill it by hurling a large rock or chunk of ice at its head.

These stories were first encountered by explorers and naturalists from Inuit guides in the 18th century. For more than two centuries until the 1990s, the accounts of polar bear hunting techniques were regarded as apocryphal — as baseless as tales about the bears using shape-shifting abilities.

But a team of researchers from Canada, the US, and Greenland, including University of Alberta biologist Ian Stirling, suspected that there might be some basis besides the reports, which have continued to this day.

Combing through direct and indirect reports from the past and recent literature and data, they reported their findings in a paper published in the June edition of the science journal "Arctic." They concluded that it was rare — but possible — for polar bears to use tools when hunting walruses.

his April 13, 2004 photo shows a large Pacific bull walrus on ice in the Bering Sea off the west coast of Alaska. (provided by the US Fish and Wildlife Service)
his April 13, 2004 photo shows a large Pacific bull walrus on ice in the Bering Sea off the west coast of Alaska. (provided by the US Fish and Wildlife Service)
Answering brute force with cunning

The first eyewitness account of the phenomenon appears in "Fauna Groenlandica," a 1780 book by Otto Fabricius, who worked as a missionary and naturalist in Greenland. In his book, he wrote, "The polar bear attacks seals and walruses in particular, using cunning against the strength and massive tusks of the walrus. It will grab a chunk of ice and throw it at the walrus' head, and then kill it while it is reeling from the blow."

Other accounts would report the same kind of story as second-hand information. But quite a few reported them as coming directly from the Inuit hunters who accompanied the writers. Typically, they described the bears as stealing up on groups of reclining walruses, climbing up on an icy slope, grabbing a large chunk of ice with both hands, standing up on their hind legs, and bludgeoning one of the walruses before rushing down to finish it off.

Engraving, made by Chukchi carvers in the 1940s on a walrus tusk, depicts a polar bear hunting a walrus. (Wikimedia Commons)
Engraving, made by Chukchi carvers in the 1940s on a walrus tusk, depicts a polar bear hunting a walrus. (Wikimedia Commons)

The reports continued all the way through the 1990s. In northeast Greenland, a 44-year-old, highly experienced Inuit hunter from Qaanaaq discovered a walrus that had been freshly killed by a polar bear.

From tracks in the snow and other evidence nearby, he speculated that a polar bear lurking near an opening in the ice had bludgeoned a female walrus with a chunk of ice. The walrus' skull was shattered, with a bloody, smoothed chunk of ice next to the animal.

The researchers noted independent but very similar reports of the polar bears' hunting behavior from Inuit hunters dating back over 240 years.

"As field scientists, our personal experience over several decades of working with Inuit hunters in Canada and Greenland is that [. . .] reports of direct observations of wild animals by experienced individual Inuit hunters are highly reliable," the researchers wrote.

GoGo, a male polar bear at the Tennoji Zoo in Osaka, Japan, uses tools to fetch food that's out of his reach. (provided by the Tennoji Zoo)
GoGo, a male polar bear at the Tennoji Zoo in Osaka, Japan, uses tools to fetch food that's out of his reach. (provided by the Tennoji Zoo)
Two-handed throw "like shooting a basketball"

As a basis for their conclusion, the researchers cited the fact that polar bears and their close relatives, brown bears, are highly intelligent animals that often use tools. An example of this is GoGo, a 5-year-old male polar bear at the Tennoji Zoo in Osaka, Japan.

To enrich the bear's otherwise monotonous life at the zoo, a chunk of meat was suspended three meters over its pool, and the animal was given various tools to reach it. In a behavior enrichment program lasting for a decade since 2010, GoGo used long sticks and other tools to retrieve the food.

In the end, however, his preferred approach was to use a hard, round object, which he would throw "very accurately" at his target with both hands in a manner "much like shooting a basketball." It's an approach with parallels to hurling of ice chunks at walrus heads.

A polar bear feeds on a bearded seal. (Wikimedia Commons)
A polar bear feeds on a bearded seal. (Wikimedia Commons)

The researchers also pointed to environmental conditions as another factor encouraging tool use by polar bears.

Male walruses can weigh up to 2,000 kilograms, and the animals have hides measuring 2–4 centimeters in thickness, as well as thick skulls. They are not as easy to kill as seals, and some polar bears have ended up gored to death with their large tusks.

Describing walruses as a "substantial but dangerous food source," the researchers noted the possibility that a "small number of [polar bears] might make the conceptual mental link between the need for a potential tool that might facilitate an improvement of hunting success and a possible solution." They also suggested the possibility that the use of tools might be passed down over generations.

Because of climate change, polar bears are facing greater difficulties hunting seals, which are their chief prey. But walruses appear unlikely to provide much of a viable alternative.

According to the researchers, reports of bears using tools to hunt walruses are found only in certain regions, including the eastern Canadian Arctic and southwestern Greenland, and their "primary focus is on calves and younger (smaller) animals."

By Cho Hong-sup, environment correspondent

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