Polar bear energy levels
POLAR BEARS ALREADY FIND IT HARD TO CATCH ENOUGH PREY – AND HOW WILL CLIMATE CHANGE AFFECT THAT?
These carnivores use up far more strength while hunting than expected
Polar bears use up far more energy while hunting than expected, new research has revealed, leading to fresh concerns about the species’ long-term viability.
Scientists attached GPS and video-equipped collars and loggers with accelerometers to nine female bears for up to 11 days over two consecutive years to find out how much effort they expended during the key hunting season of early April.
The results showed the bears’ metabolic rates were 60 per cent higher than previously assumed, and four of the nine bears lost about 10 per cent of their body mass during the study.
Lead researcher Anthony Pagano, of the US Geological Survey (USGS), says the biggest factor was the bears walking vast distances looking for seals’ breathing holes, which is how most of them catch their prey.
“Some of the bears were moving 250km over the course of 10 days,” Pagano says. “It’s not unusual for polar bears to cover big distances, but now we can quantify it – and it was the biggest factor [in their energy expenditure].”
In the paper published in Science, Pagano and his colleagues calculated that a female bear in early spring would need to catch one adult ringed seal, three subadults or 19 new-born pups every 10-12 days in order to meet their energy requirements.
But, in fact, they must really catch more than this during the key hunting period of late March to early July, before the sea ice starts to break up and deny them access to seals on which they depend. Even the refreezing of the sea ice in the autumn doesn’t suddenly provide new hunting opportunities.
“By November, seals are not as reliant on sea ice. They’re just making holes to breathe through, and they are more diligent and less naive,” Pagano says.
“As sea ice becomes increasingly short-lived annually [because of the impacts of climate change], polar bears are likely to experience increasingly stressful conditions and higher mortality rates,” the study concludes.