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Παρασκευή 17 Ιουλίου 2015

Polar Bears Don’t Go Into Hibernation...



Scientists have long considered the possibility that polar 
bears entera kind of walking hibernation to cut down their 
energy demands duringthe 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.
He also found that the bears cooled a part of their body core while swimming 
in icy water, which was a surprise. It may have to do with keeping deeper, 
more essential parts of the core warm, he said, but more information is 
needed for a full understanding of the phenomenon.
nytimes.com

[...] The Arctic ice is melting earlier each summer and freezing 
later each winter, limiting the animals' chances to catch seals. 
With no way to save energy, polar bears are unlikely to survive the 
continued sea-ice loss2 caused by rising temperatures, 
says Merav Ben-David, a wildlife ecologist at the University 
of Wyoming in Laramie and a co-author of the study.
The research suggests that the bears do not use a strategy known as 
walking hibernation-a state of lowered activity and slowed metabolism-
to survive summer fasts as some had suspected3. Instead, they show 
a smaller decrease in their metabolic rate, 
similar to that seen in any mammal with a restricted diet.... [...] 
nature.com

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