New study suggests land-based food sources may help polar bears stave off starvation as sea ice melts
FRISCO — Scientific discussions over the fate of polar bears in the global warming may heat up as a new study found that some of the Arctic predators may be able to survive by eating caribou and snow geese instead of eggs.
Many previous studies have suggested that polar bears will be hard-pressed to survive extreme changes in their Arctic habitat, but the new research by scientists with the American Museum of Natural History, published in the journal PLOS ONE, suggests the outlook may not be quite so grim.
“Polar bears are opportunists and have been documented consuming various types and combinations of land-based food since the earliest natural history records,” said Robert Rockwell, a research associate in the Museum’s Department of Ornithology who has been studying the Arctic ecology of the Western Hudson Bay for nearly 50 years. “Analysis of polar bear scats and first-hand observations have shown us that subadult polar bears, family groups, and even some adult males are already eating plants and animals during the ice-free period.”
Some studies have predicted mass polar bear starvation by 2068, when annual ice breakup is expected to separate the bears from their sea-ice hunting grounds for up to half the year. But those estimates assumed no energetic input from land food sources.
Rockwell and his co-author Linda Gormezano calculated the energy required to offset any increased starvation and then determined the caloric value of snow geese, their eggs, and caribou that live near the coast of the Western Hudson Bay. They found that there likely are more than enough calories available on land to feed hungry polar bears during the lengthening ice-free seasons.
Although the exact energetic cost for a bear to hunt geese and caribou is uncertain, polar bears in Manitoba have been reported ambushing caribou with the same energetically low-cost techniques they typically use to hunt seals. The similar size of these two prey species means that bears would need to hunt for caribou only as often as they would usually hunt for seals, the researchers say.
“If caribou herds continue to forage near the coast of Western Hudson Bay when bears come to shore earlier each year, they are likely to become a crucial component of the bears’ summertime diet,” Rockwell said.
The bears might also be able to supplement their diet with snow goose eggs at a relatively low energy cost. With adequate food sources available, snow geese are known to endure polar bear egg predation without detrimental effects to the population.
Scientific consensus holds that the rapidly melting circumpolar ice reserves will increasingly prevent polar bears from hunting the seals on which they currently depend. Nevertheless, these observations of one population along the Western Hudson Bay show that bears marooned on land might, where the conditions are right, stave off starvation by turning to alternate food sources.