A fat bear is a happy bear
Fat is Survival: Assessing Polar Bear Body Condition
Lead Scientist Cate Collins discusses the importance of fat as it relates to bear survival
Fat Bear Week is coming up in early October, an annual event hosted by Katmai National Park in Alaska, home to one of the best sockeye salmon runs on Earth. The abundance of salmon leads to impressively fat grizzly bears, and each year, Katmai rangers pit these bears against each other in a tournament to determine the fattest bear. People worldwide vote, and only one bear can claim the title of champion. This year’s competition runs from October 2-8, and you can cast your vote at explore.org/fat-bear-week.
But what about polar bears? Like grizzlies, fat is essential for polar bears’ survival. Grizzly bears bulk up in the fall to prepare for a long winter hibernation. While polar bears do not hibernate, they must also put on body fat to survive a summer of fasting. The Western Hudson Bay polar bears, which we observe in Churchill, Manitoba, spend summers on land after the sea ice melts. To put on this fat, polar bears rely on blubber-rich seals. They can consume up to 20% of their body weight in a single meal, converting much of it directly into fat reserves.
So, how do we assess a polar bear’s body condition? Researchers have developed a standardized fatness index to visually score polar bears in the wild, ranging from skinny to very fat. Most of a polar bear’s fat is stored subcutaneously, right under the skin, making their body shape dramatically different depending on their fat levels. On the skinny end of the spectrum, bears appear emaciated, with visible ribs, hip bones, and vertebrae. In contrast, very fat bears have no visible bones as they are covered by a thick layer of fat, especially around the rump. Instead of a flat belly, they have a full, rounded belly.
Thanks to this index, even inexperienced observers can now classify polar bears’ fatness. Researchers who developed this scale, published in the Journal of Wildlife Management, found that training requires observing approximately six bears in each of the thin, average, and fat categories to become proficient at assessing their condition. While the extreme ends are rarer, they are also easier to identify. Guests on our one-day expeditions to Churchill can try their hand at visually evaluating the polar bears we encounter
Seasonal ice and its relationship to Polar Bear health
This summer was unusual for the Western Hudson Bay polar bears. A high-pressure weather system caused stronger-than-usual east-to-west winds across the bay, pushing melting sea ice towards the coast, as seen in the NASA Earth Observatory photos below. While some areas of Hudson Bay lost ice earlier than expected, this ice pile-up allowed the bears of Western Hudson Bay to hunt seals for longer. This means that the polar bears we see during our 2024 fall expeditions may be in better body condition, having fasted for fewer months than in previous years.
As we head into another Fat Bear Week for grizzlies, it is a reminder that body fat is a critical measure of survival for all bear species. For polar bears, fat reserves mean the difference between thriving and struggling in the face of changing sea ice conditions. With the unusual sea ice patterns this year, it will be interesting to observe how these shifts impact the bears we encounter on our Expeditions.
References:
Stirling, I., Thiemann, G. W., & Richardson, E. (2008). Quantitative support for a subjective
fatness index for immobilized polar bears. Journal of Wildlife Management, 72(2), 568–574.
https://doi.org/10.2193/2007-123
NASA Earth Observatory. (2024). A split spring for Hudson Bay sea ice.
https://earthobservatory.nasa.gov/images/153118/a-split-spring-for-hudson-bay-sea-ice
Polar Bears International. (2024, July 9). Unusual summer in Hudson Bay: What does it mean
for polar bears? https://polarbearsinternational.org/news-media/articles/unusual-summer-in-
hudson-bay-what-does-it-mean-for-polar-bears
Explore.org. (2024) Fat Bear Week. https://explore.org/fat-bear-week
About Gold Star Canadian Tours
At Gold Star Canadian Tours, we focus on providing the worlds best travel experiences to authentically Canadian destinations. Our flagship tour is a convenient 1-day Polar Bear Expedition with dedicated non-stop charter flights from major airports directly to Churchill, Manitoba. With Gold Star Canadian Tours, the wonders of the Arctic are closer than ever. Your Adventure Awaits!
