Arctic polar bears may be adjusting their eating habits as their sea ice habitat melts and the furry white predators stand to lose the floating platform they depend on to hunt seals, their primary food. According to researchers, however, the bears are displaying flexible eating habits as their world changes around them.
Indeed, scientific studies indicate polar bear populations are falling as the sea ice disappears earlier each spring and forms later in the fall. But a series of papers based on analysis of polar bear poop released over the past several months indicate that at least some of the bears are finding food to eat when they come ashore, ranging from bird eggs and caribou to grass seeds and berries.
"What our results suggest is that polar bears have flexible foraging strategies," Linda Gormezano, a biologist at the American Museum of Natural History in New York and a co-author of several of the papers, told NBC News.
The results stem from research in western Hudson Bay, near Chruchill, Manitoba, Canada, which is in the southern extent of polar bear habitat and serves as a harbinger of what the animals are likely to face throughout their Arctic range as the climate continues to warm and sea ice breaks up earlier and earlier each spring.
The flexible foraging strategy of polar bears "means that there may be more to this picture in terms of how polar bears will adjust to changing ice conditions" than indicated by models based on the spring breakup date of the sea ice and thus their access to seals, Gormezano said.
She added that nobody knows for sure how well polar bears will adapt to the changing food supply, but a big step toward an answer is to study what they eat on land "rather than assume that they may just be fasting."
Let them eat car partsIn addition to berries, birds and eggs, Andrew Derocher, a University of Alberta polar bear biologist who was not involved with the recent studies, said people have seen a polar bear drink hydraulic fluid as it was drained out of a forklift, chomp the seats of snow machines, and eat lead acid batteries.
"Polar bears will eat anything," he told NBC News. "The question is: Does is it do them any good? And everything we can see from what bears eat when they are on land is it has a very, very minimal energetic return relative to the cost."
Gormezano said the plants found in any given pile of poop were usually the same, suggesting the bears eat whatever they find in their immediate surroundings — they don't spend a lot energy searching for food. Mothers and cubs, who wander farthest inland, feast on berries found there. On the coast, where adult males linger, the poop is predominantly shoreline grass seeds.
Animal remains, however, showed no pattern, which fits with a landscape rich with nesting birds and caribou and polar bears opportunistically eating whatever crosses their path, according to a paper Gormenzano and colleague Robert Rockwell published in BMC Ecology in December 2013.
In a paper published in Polar Biology in May 2013, the researchers report observations of polar bears chasing and capturing snow geese with the efficiency of a skilled hunter — snagging one right after the other.
"We've got bears that are dying of starvation on land in the Churchill area at the end of the ice free period. These are bears that don't have enough energy coming off the sea ice."
"Previously, it had been thought that that would not be a very energetically profitable thing for a polar bear to do because they expend more energy in the chase than they get from consuming the food," Gormezano noted.
The biologist stressed that polar bears have always exhibited a flexible foraging behavior. In a study published in Ecology and Evolution in July 2013, she and Rockwell compared scat collected in recent years with scat collected 40 years earlier. "The diet overlapped tremendously," Gormezano noted.
The bears do, however, eat more migratory snow geese now, whose Hudson Bay population exploded from 2,500 nesting pairs in the 1960s to more than 50,000 today due to a boost in their food supply further south.
What's more, the polar bears come ashore a few weeks earlier due to the melting ice, which aligns with the nesting period for the geese, meaning more eggs to eat. "That's a very easy food source because they don't need to expend much energy in order to get it," she said.
No seals, no polar bearsGormenzano said she hesitates to speculate about how the polar bears will fare if the sea ice completely disappears — "that's a long way off," she noted, but added the flexible foraging they observed "could compensate for some energy deficits stemming from lost seal (hunting) opportunities."
Derocher, the polar bear biologist, said the only reason these polar bears are eating the snow geese and other plants and animals is that they still have sea ice in the winter to hunt seals and pack on the fat. Once on shore, his and other studies show, polar bears lose about 1.5 pounds per day.
"We've got bears that are dying of starvation on land in the Churchill area at the end of the ice free period. These are bears that don't have enough energy coming off the sea ice. So any resources that they by default have got while they are on land haven't been enough to change that trajectory," he said.
The most recent published population estimates for Hudson Bay polar bears is 935 as of 2004, down from 1,194 in 1987. Unpublished estimates put the current population at around 800, Derocher said. Climate models indicate that the region will be free of suitable ice for polar bears to hunt seals by the middle of this century, perhaps sooner.
"You can't just push polar bears on shore and expect them to do just fine," Derocher said.
John Roach is a contributing writer for NBC News. He started this role in November of 2005. Roach is responsible for environmental coverage on the website. Roach has also contributed to National Geographic News, MSN, and other outdoor and environment related media outlets. To learn more about him, visit his website.