With the usual food supply for the world's polar bears threatened as melting rates of sea ice accelerate, bears attempting to supplement their diets with land-based foods are having a hard time of it, researchers say.
Scientists working with the U.S. Geological Survey discovered that bears have been feeding on birds and their eggs, along with berries but say that such a land-based diet cannot make up for lessening access to the animals' traditional food source of seals hunted from sea ice.
"The bears are being forced off the ice earlier and they are not just going to sit around and wait for the sea ice to refreeze if there is something available for them to eat," says Steve Amstrup, chief scientist with Polar Bears International.
"The issue is whether or not eating these things will benefit the bears," says Amstrup, a co-author of a study published in Frontiers in Ecology and the Environment.
"The one terrestrial food rich enough to support bears is bird eggs. But the problem is that there aren't enough of those in the polar bear's range to make much of a difference," he continued.
Polar bears have evolved to survive on the fat-rich flesh of seals, surviving through winters on fat they've stored up during the summer months.
However, summer sea ice has been receding, limiting their ability to find and consume seals and forcing them to spend longer stints on land.
Adding to the question of whether land-based foods can be sufficient is evidence that only a small percentage of polar bears are taking to foraging for food alternatives off the ice, researchers say.
"Although some polar bears may eat terrestrial foods, there is no evidence the behavior is widespread," says USGS scientist and study lead author Dr. Karen Rode.
In those areas where such terrestrial feeding has been observed, the bears' condition and their survival rates have been in decline, she noted.
As polar bears are increasingly forced off the ice and onto land, they will find themselves in Arctic habitats already inhabited by grizzly bears.
"Grizzly bears and polar bears are likely to increasingly interact and potentially compete for terrestrial resources," Rode says.
The problem in an acute one, the researchers emphasize; in 2014 the USGS determined that the number of polar bears throughout Canada and Alaska had declined by nearly 50 percent.
There is little chance the bears will be able to adapt to new environments and new food sources given the pace of climate change, Amstrup says.
"We are talking temperatures being warmer in 50 years and certainly in 100 years than has ever occurred in the evolutionary history of polar bears," he says. "You can't undo a million years of evolution in 50 years."
