New research suggest polar bears that are being forced onto land by sea ice loss are eating terrestrial foods, and this strategy may not be sustainable.
Some polar bears are believed to have expanded their palettes to include berries, birds, grains, and eggs, the United States geological Survey reported. These foods are not likely to be able to compensate for the absence of lipid-rich seals, which are polar bears' typical prey.
"Although some polar bears may eat terrestrial foods, there is no evidence the behavior is widespread," said Karyn Rode, lead author of the study and scientist with the USGS. "In the regions where terrestrial feeding by polar bears has been documented, polar bear body condition and survival rates have declined."
Many of these terrestrial regions are already inhabited by grizzly bears, but only at low densities due to due to food scarcity.
"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," Rode said. "Grizzly bears and polar bears are likely to increasingly interact and potentially compete for terrestrial resources."
Terrestrial food is much less energetically dense than marine prey, and polar bears are believed to consume the highest lipid diet of any species on Earth. Foods found in the terrestrial environment tend to be rich in protein but low in fat. Polar bears are not "physiologically suited" to ingest plants, especially in large enough quantities to sustain their large body sizes.
"The reports of terrestrial feeding by polar bears provide important insights into the ecology of bears on land," Rode said. "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 were published in a recent edition of the journal Frontiers in Ecology and the Environment.
