Polar Bears May Not Survive with Land-Based Food

Polar bears may not be able to rely on land-based food, according to a new study. As climate changes as sea ice melts, these bears are forced to eat terrestrial foods which may not be giving the animals enough calories to survive.

With warmer temperatures, sea ice is melting. This means that it's harder for polar bears to access their traditional prey, ice seals. Instead, the bears have to hunt in other locations, such as terrestrial habitats that are already occupied by grizzly bears.

Few foods are as energetically dense as marine prey, which are high in fat. Previous studies have suggested that polar bears consume the highest lipid diet of any species. Prey in terrestrial environments, though, consists of high-protein and low-fat animals and vegetation. Polar bears are not able to properly digest plants, and it would be difficult for them to gain enough fat from a terrestrial-only environment.

"Although some polar bears may eat terrestrial foods, there is no evidence the behavior is widespread," said Karyn Rode, one of the researchers, in a news release. "In the regions where terrestrial feeding by polar bears has been documented, polar bear body condition and survival rates have declined."

In this latest study, the researchers found that fewer than 30 individual polar bears have been seen consuming bird eggs from any one population, which typically range from 900 to 2,000 individuals. In other words, the behavior isn't all that common, and is unlikely to have population-level impacts on trends in survival.

"The reports of terrestrial feeding by polar bears provide important insights into the ecology of bears on land," said Rode. "In this paper, we tried to put those observations into a broader context. Focused research will help us determine whether terrestrial foods could contribute to polar bear nutrition despite the physiological and nutritional limitations and the low availability of most terrestrial food resources. However, the evidence thus far suggests that increased consumption of terrestrial foods by polar bears is unlikely to offset declines in body condition and survival resulting from sea ice loss."

The findings show that while polar bears may be able to gain some calories from land-based sources, it's unlikely they'll get their full amount of calories.

The findings are published in the journal Frontiers in Ecology and the Environment.

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