Even adapted polar bears are threatened with starvation
During ice-free periods, many of the large land carnivores are at great risk, although they can adapt their diet and their hunting and foraging behavior. This is shown by a new study.
Hardly any other animal represents the devastating consequences of global warming like the polar bear. The lengthening ice-free phase in the Arctic is making things difficult for predators. This is shown by a complex study in which researchers closely observed 20 polar bears in Canada over several weeks. The team led by Anthony Pagano from the Alaska Science Center discovered that the polar bears also search for food on land, but are less successful and therefore lose weight. The team recently published the study in the journal Nature Communications .
Advancing climate change is leading to a decline in sea ice in the Arctic. This is a problem for polar bears because they hunt seals on the ice from late spring to early summer, which give birth to their pups at this time. If the sea ice retreats, polar bears are forced to go on land. Due to global warming, the ice-free periods have lengthened significantly: from 1979 to 2015 by three weeks, so that polar bears now spend 130 days a year on land.
Polar bears are adaptable and occasionally hunt prey on land. But if the ice-free period continues to lengthen, scientists fear that the survival of the animal species will be severely endangered. According to estimates, 22 to 67 percent fewer young animals could be born by 2050. Other researchers assume that a quarter of males will starve if the Arctic sea remains ice-free for 180 days.
Despite these assumptions, it is unclear whether polar bears could survive longer during the sea ice-free period by using less energy or finding new food sources. To find out, Pagano's team examined 20 polar bears in Canada's Hudson Bay during the sea ice-free period. The authors determined the animals' daily energy consumption and changes in their body mass. Using GPS trackers equipped with a camera, the researchers were able to observe how the animals behaved, what they ate and how much they moved.
Lost up to 36 kilos
“We observed very different behaviors among the polar bears,” said Pagano, according to a Washington State University press release. “Some bears simply lay down and used as little energy as when they hibernate. Others actively foraged, subsisting on bird and caribou carcasses, seaweed and berries. Three animals even swam several kilometers through the sea to look for food."
Depending on the activity, the researchers found large differences in the animals' daily energy consumption. Overall, 19 of the 20 polar bears lost weight: 0.4 to 1.7 kilograms per day and thus 8 to 36 kilograms within the three-week observation period. It was said that some animals could have found food. But they only gained as much energy from eating as they used to search for food. Not enough to keep your strength up.
Some experts had assumed that polar bears on the mainland would behave like their relatives, the grizzly bears: they either go into rest mode or look for food on land. But that is apparently not the case. “Polar bears are not grizzlies with white fur. “They are very different from each other,” said co-author Charles Robbins, director of the Washington State University Bear Center. “Polar bears are larger and also weigh significantly more. To maintain their weight, they eat the energy-rich fat of seals - which they catch on the sea ice.
Conflicts between polar bears and humans
Although polar bears can adapt their behavior, the results highlight how a longer period without sea ice increases the risk of the animals starving. “Because polar bears have to retreat to the mainland earlier, they also have less time to build up energy reserves that are essential for survival,” says Pagano. “We assume that more animals will starve to death in the future, especially younger polar bears and females with cubs.”
The nature conservation organization WWF pointed out that the development can also have an impact on people. “The more time polar bears spend on land, the greater the risk of interactions and conflicts with people in Arctic coastal communities,” the organization said. As large predators, polar bears pose a significant threat to the local population. “Encounters can result in property damage, injuries and loss of life for both people and bears.”
According to Pagano's experts, the polar bears in western Hudson Bay are probably more affected by the consequences of climate change than those in other regions in the Arctic.
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