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Fear not, says researcher: many animals do well despite warmth

A warm December will not significantly affect the natural hibernation patterns of all animals, says one bat specialist. Bears, ants and bats, for instance, are not significantly troubled by a 10 degree Celsius shift in temperature, but coat-changing hares might be in more danger.

Lepakko (vesisiippa) puun rungolla.
A bat resting on a tree bole. Image: Minna Rosvall / Yle

Bats, bears and ants are all species that winter in Finland by hibernating or lying dormant when temperatures approach freezing.

Sightings have been made of bats swooping around this December, perplexing some onlookers. But bat specialist Nina Hagner-Wahlsten, who has studied bats for several decades, says that warm weather is not an issue for the winged mammals.

Only some few individual bats may awaken from their slumber in search of food or a better locale for their dormancy.

"Hunting for food can be a little tricky in that there aren't many insects around in December and hunting requires energy," Hagner-Wahlsten, chief of the BatHouse specialist centre says. "But I think these reported bats were just in search of a new cave or attic to hibernate in. Switching places over the winter is quite normal."

Bears rarely affected, hares more so

A warm December will likewise not make Finnish bears stir from their sleep, because a bear's den remains at warm temperatures despite the outdoor chill, or lack thereof.

Snowless and especially wet conditions, however, may drive a bear to wake up.

"If water gets into the den the bear may leave," says South-Eastern Finland's game manager Erkki Kiukas. "Usually a bear will be able to find a suitably dry place, though."

Bears typically build their den in the remains of anthills. Ants may, in fact, be found sharing a bear's wintering hole on the lowest levels.

"Ants hibernate no matter what the temperature, but even if they were to wake they wouldn't disturb a huge bear, an animal that is used to clawing out litres of honey without taking notice of angry bee stings," says chief Kimmo Saarinen from the Southern Karelia Allergy and Environment Institute. "It's far more likely that changes in weather will affect humans, not other animals."

But Kiukas says there are a few species that rely on the uniformity of their habitats.

"The fur of the mountain hare changes white automatically at the end of the year, and now predators will be able to spot them easily in the snowless terrain," he says.

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