Local weather change is stretching the size of time elements of the Far North go with out sea ice, which polar bears depend on to hunt their most well-liked prey: blubbery, calorie-rich seals. When the ice melts in summer season, the bears transfer onto land and face two choices. They’ll relaxation and decelerate to a state approaching hibernation, or they will forage for different meals like berries, fowl eggs and small land animals.
Scientists monitoring 20 polar bears in Manitoba, beneath the Arctic Circle on the southern finish of the animals’ vary, discovered that the choice the polar bears selected didn’t make a lot distinction. Bears who foraged usually bought simply sufficient energy from their small meals to replenish the power they spent discovering them, however not sufficient to take care of their physique mass.
“Terrestrial meals aren’t satisfactory to delay the interval that polar bears can survive on land,” mentioned Anthony Pagano, a wildlife biologist on the U.S. Geological Survey and the lead writer of a examine primarily based on the analysis, published on Tuesday in Nature Communications.
In western Hudson Bay, the ice-free interval is three weeks longer now than it was within the Nineteen Seventies, and polar bears at the moment spend about 130 days on land throughout the yr. Scientists estimate that, going ahead, there shall be 5 to 10 extra days with out sea ice every decade.
The query of whether or not polar bears can survive for longer durations on land has been politicized at instances because the creatures grew to become a logo of local weather change.
A 2015 evaluation by the International Union for the Conservation of Nature discovered a excessive chance of the worldwide polar bear inhabitants declining by greater than 30 % by 2050. This native inhabitants in Hudson Bay could have shrunk by half already, from an estimated 1,200 bears within the Nineteen Eighties to about 600 bears in 2021.
Practically all of the bears adopted within the new examine misplaced weight, and two people have been on monitor to starve earlier than the ocean ice returned.
Anecdotal observations of particular person polar bears consuming geese, geese, seabird eggs and even caribou on land have provided hope that the animals might adapt to a hotter world. However analysis merely documenting what polar bears are consuming hasn’t been sufficient to determine whether or not the bears get sufficient energy from that meals to assist them survive longer durations with out sea ice.
For this examine, Dr. Pagano and colleagues traveled to Wapusk Nationwide Park in northern Manitoba. Over three summers, they captured 20 polar bears and fitted them with video cameras on collars to offer bear’s eye views of their days.
The scientists weighed the bears, took blood samples and measured their respiration to color detailed footage of their physique circumstances, ranges of exercise and power expenditure. They recaptured every bear after about three weeks, retrieving the cameras and repeating their measurements.
Placing cameras on polar bears is a brand new method, and going by the video was “superb,” Dr. Pagano mentioned. “To observe what a polar bear is definitely doing within the wild was actually gratifying.”
Six of the bears (fewer than the scientists had anticipated) appeared to relaxation and quick, whereas the others foraged and some even went on long-distance swims.
The foraging bears have been principally seen consuming grass, kelp and berries, with occasional fowl carcasses, bones, caribou antlers, eggs and small mammals. Two of the swimmers discovered seal and beluga whale carcasses, however couldn’t eat a lot whereas swimming in open water.
No matter whether or not the bears fasted or foraged, all besides one misplaced related quantities of weight. The scientists calculated a “predicted date of hunger” for every bear primarily based on how a lot physique fats and muscle it had, and the way a lot power it was estimated to be expending every day.
Most have been predicted to be superb till the ocean ice returned in November, however two younger females, which are usually the smallest polar bears, had predicted dates of hunger earlier than then, and some others have been near that point. (The researchers needed to go away in September and don’t know what in the end occurred to the bears.)
Dr. Pagano famous that the examine didn’t embody any females with cubs, who burn rather more power whereas nursing. The researchers did embody some pregnant bears, however left earlier than they gave delivery.
These findings are “what we feared and what we hoped to not see,” but additionally considerably anticipated, mentioned Melanie Lancaster, a conservation biologist who focuses on Arctic species on the World Wildlife Fund.
Dr. Lancaster, who wasn’t concerned within the examine, cautioned that these 20 bears solely signify one inhabitants in a single area. “Polar bears aren’t experiencing the consequences of local weather change uniformly throughout the Arctic,” she mentioned. At greater latitudes the place thicker sea ice persists over a number of years, polar bears are nonetheless doing properly.
However for this declining inhabitants in Hudson Bay, the person variability the researchers discovered is critical, mentioned Gregory Thiemann, an affiliate professor at York College in Toronto who research Arctic carnivores however wasn’t concerned on this analysis.
Every polar bear tried in its personal solution to cope, however the variation reveals that there isn’t one profitable answer. “It paints a collective image that this can be a group of bears type of stretched to their organic limits,” he mentioned.