Arctic warming forces polar bears to adjust their diets

Jonathan Marker | Science Recorder | January 22, 2014

Arctic warming forces polar bears to adjust their diets

Polar bears are exhibiting flexible foraging behavior.

According to a January 21 news release from the American Museum of Natural History (AMNH), a three-part study of Hudson Bay polar bears by scientists at AMNH found strong evidence that Arctic warming is causing the animals to turn to alternate food sources.

As polar bears have a limited amount of time to hunt their historically preferred prey – ringed seal pups – Arctic warming reduces the time that polar bears can remain on the ice, and forces the animals to remain on land.  The new study indicates that at least some polar bears in the western Hudson Bay population are using alternate foraging tactics while on land, such as prey-switching and eating a mixed diet of plants and animals.

“There is little doubt that polar bears are very susceptible as global climate change continues to drastically alter the landscape of the northern polar regions,” said Robert Rockwell, a research associate in AMNH’s Department of Ornithology.  “But we’re finding that they might be more resilient than is commonly thought.”

Polar bears are listed as a threatened species under the United States Endangered Species Act, and are classified as “vulnerable” with falling populations on the International Union for Conservation of Nature and Natural Resources’ Red List.  Arctic warming is reducing the availability of their ice habitat, particularly in the spring when polar bears gain most of their annual fat reserves by consuming seal pups before heading back to shore for the summer.  The new study, led by Rockwell and Linda Gormezano, a postdoctoral researcher in the Museum’s Division of Vertebrate Zoology, surveys how polar bears might compensate for energy shortages from decreasing seal-hunting opportunities.

Altogether, the research shows that during the ice-free period, polar bears are exhibiting flexible foraging behavior.  This behavior likely stems from a shared genetic heritage with brown bears, from which polar bears divided about 600,000 years ago.

“For polar bear populations to persist, changes in their foraging will need to keep pace with climate-induced reduction of sea ice from which the bears typically hunt seals,” Gormezano said.  “Although different evolutionary pathways could enable such persistence, the ability to respond flexibly to environmental change, without requiring selective alterations to underlying genetic architecture, may be the most realistic alternative in light of the fast pace at which environmental changes are occurring.  Our results suggest that some polar bears may possess this flexibility and thus may be able to cope with rapidly changing access to their historic food supply.”

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