By James Gorman / Source: nytimes

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Scientists have long considered the possibility that polar bears enter a kind of walking hibernation to cut down their energy demands during the summer, when food on land is scarce.

Some research supported this idea, and a web search will find it stated as fact on some sites. But a new multiyear study that monitored the temperatures of bears living on ice and on land found no evidence of the sharp drops in body temperature that signal a decrease in the need for food in the summer.

“We didn’t find anything that looks like hibernation,” said John P. Whiteman, a biologist at the University of Wyoming, who did most of the research.

Andrew Derocher, a bear biologist at the University of Alberta and a scientific adviser to Polar Bears International, an organization devoted to polar bear conservation, said the findings added to concerns about polar bears’ futures because food sources on land are more scarce compared with the seals the bears eat when they are on the ice.

A hibernation state would be a potential physiological defense to help them cope with the reduced food sources on land during summers that are becoming longer because of climate change.

A report on the research was published Thursday in the journal Science by Dr. Whiteman, along with Henry J. Harlow and Merav Ben-David, who are also biologists at Wyoming, and other researchers with the United States Geological Survey, the United States Fish and Wildlife Service, both in Anchorage, and Polar Bears International. Dr. Derocher was among the scientists who were asked by the journal to review the paper before its publication.

Dr. Whiteman said that the most important aspect of the study was that it gathered a range of information on bear physiology during the bears’ summers on land and on ice over several years.

“This data did not exist at all,” he said, because it was so hard to obtain. The researchers used helicopters and a United States Coast Guard icebreaker to find and dart the bears with tranquilizers. The study was done in the Beaufort Sea, north of Alaska and Canada, and on its coast.

The researchers set up wind screens and lights, Dr. Whiteman said, “trying to recreate an animal surgical suite in the field.” They inserted devices into the abdomens of 10 bears to record body temperature. They also used collars to track location and activity levels, and inserted temperature recorders into the rumps of some bears.

About two dozen bears were studied in all, with the overall goal of getting a better picture of the physiology of polar bears in the summer. The researchers also took body measurements and fur and blood samples.

“We’ve got years and years of working with this data ahead of us,” he said.

Walking hibernation is only one issue addressed in the research, and Dr. Derocher said that the study refined the understanding of what bears go through. He said he still thought the term was useful because hibernation refers to a spectrum of changes that occur in different animals.

He noted that the new study showed that the polar bears do not reduce their body temperatures or energy needs in the way that other species of bears did while hibernating in dens.

But, he said, past research shows that polar bears undergo some physiological changes in the summer in the way they reincorporate some chemicals into their bodies that would normally be excreted as waste. That helps them avoid some of the damages that a human would suffer with the kind of fasting and weight loss many bears undergo in the summer. Dr. Whiteman’s study did not address those physiological studies.

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