Is that polar bear getting enough to eat? Try a collar with a camera.

Climate change is extending the time when parts of the Far North will be without the sea ice that polar bears rely on to hunt their favorite prey: blubbery, high-calorie seals. When the ice melts in the summer, the bears move to land and they have two options. They may rest and slow down into a state approaching hibernation, or they may forage for alternative foods such as berries, bird eggs, and small land animals.

Scientists who monitored 20 polar bears in Manitoba, below the Arctic Circle at the southern end of the animals' range, found that the option the polar bears chose didn't make much difference. Bears that foraged generally got just enough calories from their small meals to replenish the energy they spent finding them, but not enough to maintain their body mass.

“Terrestrial foods are not sufficient to extend the period during which polar bears can survive on land,” said Anthony Pagano, a wildlife biologist at the US Geological Survey and lead author of a study based on the study. published Tuesday in Nature Communications.

In the western Hudson Bay is the ice-free period now three weeks longer than in the 1970s, and polar bears currently spend about 130 days on land each year. Scientists estimate that there will be five to 10 days without sea ice every decade in the future.

The question of whether polar bears can survive on land for extended periods of time has sometimes been politicized as the creatures have become a symbol of climate change.

A 2015 review by the International Union for Conservation of Nature has found a high probability that the global polar bear population will decline by more than 30 percent by 2050. This local population in Hudson Bay may already have shrunk by half, from an estimated 1,200 bears in the 1980s to about 600 bears in 2021.

Nearly all of the bears tracked in the new study lost weight, and two individuals were on their way to starvation before sea ice returned.

Anecdotal observations of individual polar bears eating ducks, geese, seabird eggs and even caribou on land have offered hope that the animals could adapt to a warmer world. But research that simply documents what polar bears eat isn't enough to find out whether the bears get enough calories from that food to help them survive longer periods without sea ice.

For this study, Dr. Pagano and colleagues to Wapusk National Park in northern Manitoba. Over three summers, they captured twenty polar bears and fitted them with video cameras on collars to provide a bear's perspective of their days.

The scientists weighed the bears, took blood samples and measured their breathing to paint detailed pictures of their body condition, activity levels and energy expenditure. They recaptured each bear after about three weeks, retrieved the cameras and repeated their measurements.

Placing cameras on polar bears is a new technique, and watching the video was “amazing,” said Dr. Pagano. “It was really satisfying to see what a polar bear does in the wild.”

Six of the bears (fewer than the scientists expected) appeared to be resting and fasting, while the others foraged and a few even went swimming long distances.

The foraging bears were usually seen eating grass, kelp and berries, with occasional bird carcasses, bones, caribou antlers, eggs and small mammals. Two of the swimmers found carcasses of seals and beluga whales, but were unable to eat much while swimming in open water.

Regardless of whether the bears fasted or foraged, all but one lost the same amount of weight. The scientists calculated a “predicted date of starvation” for each bear based on the amount of body fat and muscle it had, and how much energy it estimated it would expend each day.

Most were predicted to be fine until sea ice returned in November, but two young females, who tend to be the smallest polar bears, had predicted a famine earlier, and a few others were around that time. (The researchers had to leave in September and don't know what ultimately happened to the bears.)

Dr. Pagano noted that the study did not involve females with cubs, which burn much more energy while breastfeeding. The researchers did take in some pregnant bears, but left before they gave birth.

These findings are “what we feared and what we hoped we wouldn't see,” but also somewhat expected, says Melanie Lancaster, a conservation biologist who specializes in Arctic species at the World Wildlife Fund.

Dr. Lancaster, who was not involved in the study, cautioned that these 20 bears represent just one population in one region. “Polar bears are not experiencing the effects of climate change in the same way across the Arctic,” she says. At higher latitudes, where thicker sea ice persists for several years, polar bears still thrive.

But for this declining population in Hudson Bay, the individual variability the researchers found is significant, says Gregory Thiemann, an associate professor at York University in Toronto, who studies carnivores in the Arctic region but was not involved in this research.

Each polar bear tried to deal with it in its own way, but the variation shows that there is no one winning solution. “It paints a collective picture that this is a group of bears that are more or less stretched to their biological limits,” he said.