As polar bears are forced on shore due to increasing sea ice loss, the animals are turning to berries, birds and eggs to supplement their diet.
Polar bears usually prey on fat-rich ice seals, and the new snacks are unlikely to compensate for lost opportunities to eat seals, according to research from the US Geological Survey.
‘Although some polar bears may eat terrestrial foods, there is no evidence the behaviour is widespread,’ says Dr Karyn Rode, who led the research into polar bear diets. ‘In the regions where terrestrial feeding by polar bears has been documented, polar bear body condition and survival rates have declined.’
Polar bears are also encroaching into grizzly bear territory when foraging on land, the study says. Life is already tough for grizzlies in those ranges, with bears found to be the smallest of their species due to poor food availability and quality. Competition from displaced polar bears is likely to be unwelcome.
‘The smaller size and low population density of grizzly bears in the Arctic provides a clear indication of the nutritional limitations of onshore habitats for supporting large bodied polar bears in meaningful numbers,’ says Rode. ‘Grizzly bears and polar bears are likely to increasingly interact and potentially compete for terrestrial resources.’
So far only 30 polar bears have been seen eating bird eggs. ‘There has been a fair bit of publicity about polar bears consuming bird eggs. However, this behaviour is not yet common, and is unlikely to have population-level impacts on trends in body condition and survival,’ adds Rode.
Polar bears consume more fats than any other species. On land, polar bears are only likely to find high-protein, low-fat animals and vegetation. Polar bears are unable to digest plants, and it would be difficult for the bears to consume a high enough protein volume to support their bodies.
Whatever polar bears manage to forage on land, it is unlikely to offset losses from seal hunting.