A climate change diet for polar bears is a losing proposition, a new study suggests.
As Arctic sea ice shrinks due to climate change, many polar bears are forced to shift their diet to land during parts of the summer. A study examining Hudson Bay polar bears is trying to figure out whether they can maintain their fat figures, which is what’s needed, and found that a large portion of them lost weight no matter what they did to strengthen their bodies. weight.
Some bears find lots of food—berries, eggs, seabirds, and even caribou antlers—but it takes so much effort that so many calories are burned trying to eat that they end up losing weight and expending more energy than they take in. According to a study in Tuesday’s journal Nature Communications.
Other bears semi-hibernate, not doing much, but also losing weight, so neither method works, said the study’s lead author, U.S. Geological Survey wildlife biologist Anthony Pagano.
Researchers found that 19 of 20 bears studied in the study, which tracked calorie intake, energy use and respiration in the wild, dropped an average of 47 pounds (21 kilograms) over three weeks. This means losing, on average, about 7% of body mass in just 21 days, the study found.
Polar bears try to maintain their weight during the summer months after spring, when they feast tremendously and fatten up. Pagano said the lack of sea ice in the Hudson Bay region the researchers studied meant polar bears stayed on land three weeks longer than in the 1980s.
Generally, polar bears eat high-fat seals based on the sea ice near where the seals are found. Hunting is especially good in the spring, when seal pups are weaned and polar bears are easy prey before they learn to swim from the ice bottom, Pagano said.
Last September, when Arctic sea ice reached its annual low, there was about 1 million square miles (2.6 million square kilometers) less sea ice than at the same time in 1979, according to the National Snow and Ice Data Center. The United States Fish and Wildlife Service lists polar bears as a threatened species “due to loss of sea ice habitat.”
“This paper clearly shows that polar bears have not been able to adapt to the pace of change in the Arctic, and bears are using everything they already have to survive,” said Andrew Derocher, a biologist at the University of Alberta who was not part of the research. , but described it as extremely gracious and insightful.
“This is concerning because it of course raises the question of when individual bears will run out of energy,” Derocher said. While research showed some bears were doing well, “other bears were basically right on the edge of where they were potentially in danger of starvation and subsequent death.”
Derocher shows that polar bears in general are unlikely to adapt to living on land.
When polar bears have sea ice, they feast on seals. Not just the seals, but their fat too. While on ice, about 70% of a polar bear’s diet consists of fat, said USGS wildlife biologist Karyn Rode, one of the study’s authors.
“They have the highest fat diet of any species on Earth,” Rode said.
“Polar bears need sea ice to feed; that’s how they access their primary prey (ice seals),” said University of Washington biologist Kristin Laidre, who was not part of the study team. “They evolved from grizzly bears to live on a diet of marine oils and have a remarkable ability to consume and digest lipids.”
To understand what was happening on land, a joint U.S.-Canadian team of biologists put video on bears’ collars, fed the bears a type of water that allows their calorie intake and expenditure to be tracked, and sent them back into the wild to be monitored.
The bears’ hunt for food was impressive. All but one ate grass and algae, 10 ate nuts, eight gnawed bird carcasses, a third chewed bones, and four ate caribou horns, bird eggs, a rodent, and a rabbit. consumed.
However, the bears had to spend a lot of energy to feed themselves. On average, they traveled 58 miles (93 kilometers), and one young woman traveled 233 miles (375 miles) in three weeks.
“This paper adds to growing evidence that polar bears will not be able to sustain themselves on land as we continue to lose sea ice due to climate warming,” said Laidre, who chairs the International Union for Conservation of Nature expert group on polar bears. International organization that monitors the status of endangered species.
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Associated Press reporter Stephanie Windeler contributed from London.
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