Within the Arctic Circle, every now and then, the largest of all bear species hides a hard-earned kill in an icy larder. Just like a squirrel buries its nuts to save for later, polar bears have been observed burying meaty carcasses under the snow. A new study, published in Arctic Science, explores this behavior, finding that while it does occur, it is still pretty rare.
A team led by the University of Alberta set out to determine whether polar bears exhibit caching behavior and how frequently it had been observed. To find out, they trawled through thousands of observations of bears made in Svalbard, Greenland, and Canada between 1973 and 2018.
“The paucity of observations of wild polar bears (Ursus maritimus) caching of food (including hoarding, i.e., burying and remaining with a kill for up to a few days) has led to the conclusion that such behavior does not occur or is negligible in this species,” the researchers begin their paper. However, they identified 19 instances of polar bears hiding their food, suggesting that although rare, this behavior is very much present in the species.
“My curiosity about short-term food caching was re-activated by receiving a photo from a friend of a male polar bear lying on the ice with a mostly snow-covered harp seal [image a below],” study leader Dr Ian Stirling told Polar Bears International. “I had seen this kind of behavior only once in over 40 years of research on polar bears. On talking with colleagues… all had seen this behavior, but only rarely.”
It appears that hoarding behavior is influenced by features of the prey. A small snack, like a baby seal, will be gobbled down in one, leaving nothing to hoard, but a larger meal, like an adult ringed seal or part of a whale might be covered in snow and guarded by the bear while it takes a break from eating. The researchers think this is to prevent a phenomenon known as kleptoparasitism, which involves fellow bears and other scavengers getting their paws on the prize and stealing it.
The sight of a dark, bloodied carcass is quite an obvious one in a pristine white backdrop, so a covering of snow makes the kill much harder for other animals to spot. They might still be drawn to it by its smell, though. The authors note that bears are more likely to cache their prey when there’s more snow about to cover it. Some polar bears were so keen to cling onto their prey, they were observed burying it multiple times.
“When the ship was about 150 meters from the bear, it woke, dragged the carcass out from under its snow covering, left the floe he was on, swam with it to an adjacent floe, and dragged it out of the water,” notes the paper, describing one observation. “Between about 19.30 and 22.30 the bear moved the carcass several times, each time after which he slept briefly, washed his paws, fed, and re-buried the carcass.”
Another bear was sighted with an entire beluga whale calf (it probably found it dead), which it dragged off the beach and covered with grass. One bear was even seen with a half-eaten young polar bear, which it had partially covered with seaweed.
Caching behaviour has been observed in various bear species, but it’s most common in brown (aka grizzly) bears. The researchers believe that the difference in caching frequency between the two species might be linked to who they share their habitat with. Brown bears have a denser population, and share their forested homes with numerous scavengers like wolves and ravens. Polar bears, meanwhile, are more spread out and only have to deal with the occasional Arctic fox or feathered thief. Nevertheless, when you’re in possession of a whale carcass or a big juicy seal, keeping it secret is always a good idea.