Why polar bears can't survive on land

Polar bears, increasingly being forced on shore due to sea ice loss, may be eating land-based foods including berries, birds and eggs.

However, these foods cannot make up for the benefits from their traditional, lipid-rich prey - ice seals -- says a new study.

"Although some polar bears may eat terrestrial foods, there is no evidence the behaviour is widespread," said Karyn Rode, lead author of the study and scientist with the US Geological Survey (USGS).

"In the regions where terrestrial feeding by polar bears has been documented, polar bear body condition and survival rates have declined," Rode added.

In an article published in Frontiers in Ecology and Environment, the scientists noted that over much of the polar bear's range, terrestrial habitats are already occupied by grizzly bears.

Those grizzly bears occur at low densities and are some of the smallest of their species due to low food quality and availability.

Further, they are a potential competitor as polar bears displaced from their sea ice habitats increasingly use the same land habitats as grizzly bears.

"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 explained.

"Grizzly bears and polar bears are likely to increasingly interact and potentially compete for terrestrial resources," he added.

The study found that fewer than 30 individual polar bears have been observed consuming bird eggs from any one population, which typically range from 900 to 2000 individuals.

"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," Rode said.