Polar bears are the kings of the ice surface covering the top of the globe, but the ongoing loss of the Arctic sea ice on which they hunt seals is causing summer food deprivation that threatens these imposing predators.

Some experts had thought the bears might be able to mitigate the effects of reduced food intake by entering a "walking hibernation" during summers, an energy-conserving state of reduced activity and metabolic rate akin to the winter hibernation other bear species undertake.

A study released on Thursday showed this is not happening. Researchers who monitored the body temperature, activity levels and movements of 30 bears found they limited their summer energy expenditure, but not enough to compensate for the food deprivation they face.