By Dr. Becker
Polar bears live in one of the harshest environments on earth, and in order to survive they’ve got to be sure to eat enough. A typical polar bear may be lucky to catch and eat one seal every 10 days, and researchers wanted to know how they make those valuable calories last.
Seven female polar bears living near Alaska’s Beaufort Sea were fitted with devices similar to the popular wearable fitness trackers. The devices kept track of the polar bears’ movements and, along with neck cameras, gave a glimpse into the daily life of such a bear.
Polar Bears Spend Most of Their Day Resting
To conserve energy, the bears in the study spent about 70 percent of the day lounging around. They’re not lazy; they have to conserve their energy in order to survive. About 15 percent of the time they spent walking, and the rest of their waking hours was spent swimming, eating, grooming or interacting with males.
During the study period, which spanned between eight and 11 days in spring 2014 and another similar timeframe in 2015, three of the bears caught a seal to eat. The others either ate meat from old carcasses or went hungry.
The study, which was led by U.S. Geological Survey (USGS) researchers and presented at the January 2016 Alaska Marine Science Symposium, revealed what scientists had long suspected – that polar bears may have difficulty surviving if melting sea ice forces them inland.
Why Polar Bears Could Disappear Without Ample Sea Ice
Polar bears depend on sea ice to hunt their prey. For an animal that spends its days doing very little, it’s an ingenious setup.
A polar bear can wait silently at a breathing hole in the ice, then attack when a seal comes up for air. So even while hunting, a polar bear must expend very little energy for the bulk of the ‘hunt.’
As the ice disappears, however, they may be rapidly adapting to their changing environment and spending more time in the water for ‘aquatic stalks.’ Recently, researchers recorded a record-breaking polar bear dive that lasts three minutes and 10 seconds. A typical dive lasts from three to 30 seconds.
It’s thought that the bears are being forced to dive to deeper depths in order to survive. If they’re lucky, they’ll catch a seal for their efforts, but even then they’re using up far more of their calorie reserves than they’re accustomed too. The same goes for polar bears that travel inland in search of food.
USGS research biologist Anthony Pagano, who led the study, noted that in order for polar bears to hunt on land it would require a “calorie-spending chase.”
Further, other foods available on land, like goose eggs and even human trash, provides far fewer calories than a fatty seal, and are unlikely to sustain the species over time.
When asked if he though polar bears could survive if they had to switch to land-based foods, Pagano told Alaska Dispatch News, “It’s going to be pretty unlikely, I think.”1
The researchers plan to continue their polar bear surveillance in order to gain more information about polar bears’ movements and energy requirements over a full 24-hour period.
Polar Bears Can Gallop as Fast as a Horse
Polar bears are known (among other things) for their relatively slow, leisurely walk. However, if necessary, the bears can gallop as fast as a horse (up to 25 miles an hour) for a short distance.2
It’s fortunate that they don’t do this often, however, as it expends a great deal of energy and large bears may quickly overheat (even in the Arctic). Polar Bears International explained:3
“Norwegian scientist Nils Oritsland showed that polar bears expend more than twice the energy of most other mammals when walking or running—showing higher than average increases in temperature and oxygen consumption.
When their locomotion is compared with that of their closest living relative, the brown bear, polar bears exhibit what is called “a functional complex adapted to locomotion in a polar environment.
Walking bears expend 13 times more energy than resting bears. This partly explains their preference for still-hunting, which usually involves a long, patient wait for a seal to surface at a breathing hole in the sea ice.”
Ever Wonder How Polar Bears Find Each Other in the Arctic Tundra?
Considering polar bears are solitary and prefer not to walk or run if they don’t have to, you may be wondering how two such bears meet up to mate. Brown and black bears use chemical signals to find each other, often by leaving markings against objects like trees. But such objects are virtually nonexistent on the open tundra.
It turns out polar bears have a unique way of finding mates – their footprints. Chemical scents left behind in each step appear to provide a proverbial trail of breadcrumbs for the bears to follow. Unfortunately, such trails may be another factor disrupted by melting sea ice, which could fragment the trails. According to the researchers:4
“ … continuously distributed scent signals necessary for breeding behavior may prove less effective if current and future environmental conditions cause disruption of scent trails due to increased fracturing of sea ice.”