Polar bears at risk of starvation from longer summers

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These animals are unlikely to adapt to living in an ice-free environment in the Arctic. Their dietary strategies to survive during these periods do not prevent them from losing a lot of weight, according to research that has followed them using GPS and video in Hudson Bay, Canada.

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Eva Rodriguez 

The Arctic is losing sea ice rapidly due to the climate crisis and it is expected to disappear completely in the summer in the 2030s. Given this situation, an international research team, led by the Alaska Science Center, has studied how polar bears behave (Ursus maritimus) before this thaw.

To do this, they used necklaces with video cameras and GPS to track 20 polar bears during the Arctic summer season—August to September—between 2019 and 2022 in western Hudson Bay, Canada. The ice-free period in this region increased by three weeks between 1979 and 2015, keeping bears on land for about 130 days over the past decade.

The authors controlled their daily energy expenditure, The changes in body mass, diet, behavior and movement. Their goal was to find out what these ice apex predators ate and did during the prolonged time they spent on land when their preferred prey, seals, were out of reach.

 

We were able to document their behavior, weight change, energy cost, and movements, allowing us to determine that the bears displayed a variety of behaviors and strategies.

Karyn Rode, researcher at the Alaska Science Center
 
“We were able to document their behavior, weight change, energy cost and movements, which allowed us to determine that the bears showed a variety of behaviors and energy strategies while summering on land, but that these did not prevent weight loss. 19 of the 20 bears in our study lost body mass,” he tells SINC. Karyn Rode, researcher of Alaska Science Center and co-author of the study published in the magazine  Nature Communications.

Among these tactics to spend less energy are: fasting, reducing your movements and eating berries and birds. All of them were carried out regardless of age, sex, reproductive stage - pregnant females were also followed - or initial fat levels. However, they did not prevent them from losing an average of one kilogram per day. Even those who foraged lost weight at the same rate as those who lay down. Only one of them gained weight after stumbling upon a dead marine mammal.

"Our results support previous studies indicating that when polar bears spend longer periods summering on land, they lose increasingly greater amounts of weight the longer it lasts,” emphasizes the researcher.


Support conservation efforts

As sea ice continues to retreat, understanding these adaptive behaviors is critical to conservation efforts aimed at supporting polar bears in a rapidly changing ecosystem.

Between late spring and early summer, polar bears use sea ice as a platform to hunt seals mainly when they are giving birth and weaning their young.

There are some populations – of the 19 recognized throughout the circumpolar Arctic – that have access to the carcasses of marine mammals, such as whales, while they are on shore, which would help them compensate for weight loss. But in Hudson Bay, bears do not currently have these types of marine resources on land and are likely to be negatively affected by longer ice-free periods.

 

Terrestrial foods gave them some energetic benefit, but ultimately they had to expend more energy to access those resources

Anthony Pagano, wildlife research biologist
 
"He Environment and Climate Change Canada has maintained a long-term research program, which helped us closely track these animals for approximately three weeks while they were on land,” explains the scientist.

Anthony Pagano, a wildlife expert with the US Geological Survey's Polar Bear Research Program, notes that “terrestrial foods gave them some energetic benefit, but ultimately they had to expend more energy to access those resources.”

The study required collaboration between multiple organizations and agencies across international borders in order to successfully collect the data needed to better understand the behavior and energy of polar bears when they spend the summer on land.

“With land use increasing, the expectation is that we will probably see increases in famine, particularly, among the teenagers and the females with puppies,” concludes the expert.

Reference:

Anthony M. Pagano et al. “Polar bear energetic and behavioral strategies on land with implications for surviving the ice-free period.”  Nature Communications.

 
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Rights: Creative Commons.
Octavio Alonso