‘Hibernation’: Animal survival in the cold months – Gnats, moles and weasels… are shrinking

When winter comes animals do not have many options to feed themselves, while at the same time they need more energy. To get through the winter they have developed various strategies: Hibernation is perhaps one of the most well-known ways animals survive the cold months, but it is not the only way.

For example, according to the German Association for the Protection of Nature (NABU), marmots, hedgehogs and bats drastically reduce their body temperature and their bodily functions essentially stop. The term “hibernation” is therefore misleading. “Animals don’t sleep. They are in a physical state just before death,” explains biologist Thassilo Franke from the Natural History Museum in Munich. Therefore, the animals must periodically break their hibernation, making a transition to a “real sleep” in order to supply their nerve cells with oxygen, says Klaus Hacklendar of the German Wildlife Association.

Brown bears, squirrels and badgers, on the other hand, only hibernate during the winter. This means that they do not greatly disturb their metabolic system. According to biologist Hacklendar, most of these animals in the interim are active, looking for food. The brown bear spends several months during hibernation in northern regions surviving only on its fat reserves. “It’s very interesting that her muscle mass and bones don’t break down despite the long rest period,” notes Franke.

Forester of the pine forest the nutcracker

Other animals build up food stores for the coming hard times. For example, the nutcracker feeds on pine seeds in the mountains. It creates thousands of hiding places during the winter, contributing to the spread of Swiss pine. Because of the seeds that are released from the opened pine cones, they can then germinate in the hiding places that the birds created but did not have time to empty.

In contrast, deer and wild boar depend on finding food in winter, explains Angelica Nelson of the Bird and Nature Conservation Association of Hilboltstein in Bavaria. Due to the lack of food their body adapts to survive. “The volume of the rumen shrinks by 30%,” states Franke. Other animals completely change their diet and have to adapt their digestive system to cope, such as the… Moustakalis, a bird that usually feeds on insects, but in winter survives by eating reed seeds. In this way, his stomach is “reconstructed”.

Shrinkage as a precaution

Smaller animals have to expend more energy when it’s cold to maintain their body temperature. Flies, moles and weasels shrink to conserve energy. Behavioral neurobiologist Moritz Hertel of the Max Planck Research Institute points out that the fly reduces its weight by 1/5 in winter. “We observe a reversible osteoporosis” says the specialist.

Some animals have natural protection against frost. Amphibians such as frogs burrow into the ground or seek another place to protect themselves from winter and frozen waters. In sub-zero temperatures they hibernate according to biologist Nelson. In order to avoid the risk of the liquid between their cells freezing, amphibians use glycerin, which acts as an antifreeze.

Finally, many birds migrate to warmer climates to avoid the cold winter temperatures. Short-distance migrants travel as far as the Mediterranean, while long-distance migrants reach as far as Africa, biologist Nelson points out. But the journey of thousands of kilometers often turns out to be dangerous. Therefore, due to the milder winters, the migratory routes also adapt quickly.

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