Polar bears may not be able to rely on land-based food sources to survive as global warming changes the sea and ice melts, according to a new study. With the warmer temperatures, much of the ice in their habitat melts. This in turn, makes it harder for them to access their main food source, ice seals. Instead, the bears have had to turn to other sources of prey instead, hunting in areas that are already dominated by grizzly bears, placing them in direct competition with this seasoned land-based predator.
Previous studies have found that polar bears consume the highest lipid diet of any species, thanks to the high fat and energetic meal that an ice seal provides. Terrestrial food sources for the bears, however, are lower in fat, and higher in protein and vegetation. Polar bears cannot properly digest plants, and it would be difficult for them to gain enough fat from these food sources to survive.
"Although some polar bears may eat terrestrial foods, there is no evidence the behavior is widespread," coauthor of the new study, Karyn Rode says. "In the regions where terrestrial feeding by polar bears has been documented, polar bear body condition and survival rates have declined."
In this most recent study, researchers found that few than 30 individual polar bears have been seen consuming bird eggs from any one population, which typically range from 900 to 2,000 individuals. Basically, this behavior is not common and it is unlikely to have population impacts necessary to ensure their survival.
"The reports of terrestrial feeding by polar bears provide important insights into the ecology of bears on land," Rode says. "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 go on to show that while the polar bears do in fact gain some calories from consuming a more terrestrial diet, they are unlikely to get the full amount of calories they need to thrive and even survive if they are forced to focus their hunting only in these areas, due to their inability to hunt their favorite food source on the ice.
