A female polar bear and her cub snack on kelp on the shores of Hudson Bay while waiting for the sea ice to form in the fall. Such foods may fill bellies, but don’t meet the bears’ nutritional needs. Photo: Daniel J. Cox / Natural Exposures

1 April 2015 (Polar Bears International) – Scientists have known for years that polar bears forced ashore in summer by melting sea ice may feed on foods like bird eggs, berries, and small mammals. But would polar bears be able to survive in a warming Arctic by eating land-based foods?

The short answer: no.

A new study by the USGS, Washington State University, and Polar Bears International examines this question. In a paper released today in Frontiers in Ecology and the Environment, the authors show that switching to terrestrial foods isn’t a viable solution for polar bears.

“We know that polar bears have been raiding bird nests and even catching some adult geese, but the critical question is: how important is this?” said PBI’s chief scientist, Dr. Steven Amstrup, a coauthor of the paper. “There’s a difference between seeing an animal eat something and understanding what the value of that food is.”

Inadequate Diet

The research team compared the nutritional needs of polar bears, which have evolved to prey on fat-rich seals, with the nutrients available in land-based foods. They found that while some individual bears may temporarily benefit from eating energy-rich foods like bird eggs, these aren’t abundant enough to have an impact at the population level. And other possible foods, like small mammals and vegetation, don’t meet the polar bear’s nutritional requirements.

“Although some polar bears may eat terrestrial foods, there is no evidence the behavior is widespread,” said Dr. Karyn Rode, lead author of the study and a scientist with the USGS. “In the regions where terrestrial feeding by polar bears has been documented, polar bear body condition and survival rates have declined.”

Amstrup adds that the tundra niche is food-poor from a bear’s perspective.

“The brown bears already there are small and occur in low densities,” he said. “Why would anyone think this nutritionally poor environment suddenly could support whole populations of the world’s largest bears?”

“While it’s tempting to think that polar bears could survive by switching to a terrestrial diet, this paper establishes in no uncertain terms that land-based foods do not offer any hope of polar bear salvation. And, if we don’t save the sea ice, polar bears will indeed be gone.”

You can help: sign our Petition for Polar Bears, asking world leaders to take meaningful action on climate change, and ask your friends, family members, and colleagues to do the same.

Land-based Foods Not the Answer for Polar Bears

By Karyn D Rode1*, Charles T Robbins2, Lynne Nelson3, and Steven C Amstrup4

April 2015 (Frontiers in Ecology and the Environment) – Increased land use by polar bears (Ursus maritimus) due to climate-change-induced reduction of their sea-ice habitat illustrates the impact of climate change on species distributions and the difficulty of conserving a large, highly specialized carnivore in the face of this global threat. Some authors have suggested that terrestrial food consumption by polar bears will help them withstand sea-ice loss as they are forced to spend increasing amounts of time on land. Here, we evaluate the nutritional needs of polar bears as well as the physiological and environmental constraints that shape their use of terrestrial ecosystems. Only small numbers of polar bears have been documented consuming terrestrial foods even in modest quantities. Over much of the polar bear's range, limited terrestrial food availability supports only low densities of much smaller, resident brown bears (Ursus arctos), which use low-quality resources more efficiently and may compete with polar bears in these areas. Where consumption of terrestrial foods has been documented, polar bear body condition and survival rates have declined even as land use has increased. Thus far, observed consumption of terrestrial food by polar bears has been insufficient to offset lost ice-based hunting opportunities but can have ecological consequences for other species. Warming-induced loss of sea ice remains the primary threat faced by polar bears.

Can polar bears use terrestrial foods to offset lost ice-based hunting opportunities?


  1. Anonymous said...

    "Why would anyone think this nutritionally poor environment suddenly could support whole populations of the world’s largest bears?"

    Well, that's the mantra from the climate change deniers. Not known for intelligence or common sense or any understanding of science, climate change deniers will probably assume that polar bears can eat moss.

    And they do not care.

    To them, ANY discussion of climate change intrudes upon their fantasy reality of fairy tales running through their heads. Dead polar bears are just not part of the equation, where 2+2 = 3.  


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