The study, published in the journal Science, found that polar bears have a higher metabolism than previously thought.
The scientists estimated that a female bear would need to eat either one adult ringed seal, three subadult ringed seals or 19 newborn ringed seal pups every 10 to 12 days to remain in energy balance.
The problem is that many polar bears can't seem to find enough food to satisfy their high energy requirements.
They measured the metabolic rates of each bear by analyzing blood and urine samples upon capture and then again at recapture, after eight to 11 days.
"You're talking a pretty fantastic amount of mass to lose", said U.S. Geological Survey wildlife biologist Anthony Pagano, lead author of a new study in Thursday's journal Science.
For his study, Pagano, who is also a wildlife biologist with the U.S. Geological Survey, examined adult female polar bears on sea ice in the Beaufort Sea, off the north coast of Alaska.
"This study is a attractive example of how animals are built to live in synchrony with their environment".
Overall, the WWF says the five states-Canada, the United States, Russia, Denmark-Greenland and Norway-are way behind their agreed schedule for implementing the Circumpolar Action Plan: Conservation Strategy for the Polar Bear, which flowed from their 2015 agreement.
"The high energy requirements of polar bears corroborate previous hypotheses that most terrestrial Arctic habitats, lacking prey as energy-rich as marine mammals, can not provide enough food for polar bears driven to shore by loss of sea ice", Whiteman wrote in a commentary on the paper. "This study identifies the mechanisms that are driving those declines by looking at the actual energy needs of polar bears and how often they're able to catch seals".
Dangling from the neck of a polar bear, viewers can see them playfully chasing other bears, hunting seals and diving into the water. "Eventually, you run out of gas".
Environmental changes created by climate change cause polar bears to expend more energy to catch less prey, according to a harrowing new study that underscores their plight.
The Beaufort Sea population that Pagano studied has declined by about 40 percent since 2005.
This April 20, 2015 photo provided by Busch Gardens shows a polar bear wearing a Global Positioning System video-camera collar lying on a chunk of sea ice in the Beaufort Sea.
Scientists once thought that polar bears should be able to reduce their metabolic rates when there's not much food available.
As well, the bears were equipped with Global Positioning System collars that also collect video records of activity during daylight.
In the Beaufort Sea, for example, the polar bears are forced to move much greater distances than they previously did as the Arctic warms and more sea ice melts.
"We now have the technology to learn how they are moving on the ice, their activity patterns, and their energy needs, so we can better understand the implications of these changes we are seeing in the sea ice", Pagano said.
"We found a feast and starvation lifestyle - if they missed out on seals it had a pretty dramatic effect on them", said Anthony Pagano, a USGS biologist who led the research, published in Science. Previous studies found other animals are going without food longer than they did in the 1980s and 1990s, the study notes.
Pagano said the working assumption is that as the ice recedes and the bears move further North following receding ice, they will move over deep water that is less conducive to seal hunting. Less area to hunt means lower body condition for bears, which means fewer healthy cubs, which means a decline in population.
Even though the Arctic should be flush with seal pups in the month of April, the researchers found numerous bears were spending more energy chasing down prey than they consumed.
The findings put grim numbers to the reality that polar bears face as sea ice continues to retreat, researchers said.
But still, "when I see pictures of big glacial blocks breaking away and the sea ice is retreating, I get anxious", Fickel admits.
"To us, it really stressed the feast-or-famine lifestyle that these bears have", Pagano said.
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