Sea ice melts in the polar caps have raised concerns over the ability of polar bears to survive due to decreased availability of seals, but a new study has suggested that these animals won’t be starving thanks to caribou, snow geese and eggs.
Climate change is causing the polar ice to melt and this has spawned concerns that these species will be facing difficulty in keeping themselves fed. A researcher by by Linda Gormezano and Robert Rockwell at the American Museum of Natural History, however, suggests that polar bear’s extended stays on land may not be as grim as once thought and they will be able to obtain their calories from alternate food sources.
Researchers have suggested that polar bears are opportunists and there have been previous studies showing their varied eating behaviour depending on the circumstances. The researchers have also suggested based on analysis of polar bear scats and first-hand observations that polar bears are already eating plants and animals during the ice-free period.
Previous studies have also suggested that there will be mass polar bear starvation by 2068, when annual ice breakup is expected to separate the bears from their sea-ice hunting grounds for a consecutive 180 days each year–creating ice-free seasons that will last two months longer than those in the 1980s. But those estimates assumed no energetic input from land food sources.
Gormezano and Rockwell computed 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 eggs of snow geese are another food source for bears, and the energetic cost of obtaining eggs in ground nests is exceedingly low, the researchers say. 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.
