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Warm winter delays bears' hibernation

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10:33 CET+01:00
Confused by an exceptionally mild autumn Swedish bears have delayed hibernating by more than a month, leaving only a small number of the animals in search of their long winter sleep.

"We still have three or four bears that haven't decided it's time to sleep. Temperatures are above zero. The ground hasn't frozen, so they are still awake," curator at Kolmården Safari Park, Lennart Sundén told AFP.

Located 90 miles (150 kilometres) south of Stockholm, Kolmården is home to 10 brown bears that usually hibernate from the end of October until April. The region surrounding the safari park has experienced its mildest autumn since 1860, according to the Swedish Meteorological and Hydrological Institute (SMHI).

"It's not a big problem in a zoo (to delay hibernation) because we are able to keep feeding them. Of course that is the big difference with the wild bears, it could be a big problem for them not finding (enough) to eat," Sundén said.

"But our bears just delay the time they go to sleep. They have eaten enough during summer so they are big and fat enough to go to sleep," Sundén added.

There are some 2,500 brown bears living in the wild in Sweden and a further 50 in captivity.

In 1984 the Swedish Environmental Protection Agency set up a research programme devoted to brown bears in Scandinavia. In addition, for almost 20 years researchers have worked with bear experts in Norway.

With the use of radio transmitters researchers have made detailed studies of the movements of brown bears.

"We get information by radio transmitter and now all of them are going into hibernation," professor Jon Swenson, who heads the research at the Norwegian University of Life Sciences (UMB), told AFP.

"The snow is very late but they are going (into hibernation) anyway. They ate enough so they are going to their dens," Swenson added.

While temperature and the amount of daylight hours are important in dictating when bears hibernate, the most important factor is whether bears have eaten sufficient amounts to keep them going throughout their long rest, Sven Brunberg, also at UMB, said.

Food scarcity forces the bears into hibernation as they attempt to use less energy. They can not hibernate however if they have not been able to accumulate sufficient body fat to survive the winter.

In order to make it through the winter bears need around 440 pounds (200 kilogrammes) in additional weight. Prior to hibernating the animals fatten themselves up by eating as much as possible.

Pregnant females are the first to retire to their dens, followed by mothers and their cubs. Last to bed down are the males. Females have been known to hibernate from the end of September until May and even June.

"What will happen with the global warming climate is that winters get shorter and shorter and warmer and warmer. This will of course affect the bears," Swenson said.

Delayed hibernation has so far not had a detrimental effect on bears.

"They probably adapt themselves. In the long term, their hibernation could be shorter but I don't think this is necessarily negative for them," Swenson added.

"What could have a serious effect (on the bears) is if climate change affects vegetation and causes a shortage of berries, their staple food," Brunberg explained.

If bears are unable to find sufficient amounts of food to see them through their winter hibernation they are more likely to become aggressive and search for food outside their territory.

Europe's unusually warm autumn has broken records across the continent with many places reporting their warmest season in decades, and in some cases centuries.

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