These Tiny Japanese Bats Hibernate In Winter By Building Little Igloos

Evidence for Ussurian tube-nosed bats (Murina ussuriensis) hibernating in snow. Hirofumi Hirakawa/Yu Nagasaka/Scientific Reports

Bloodsucking and diseases aside, bats are extremely cute creatures. Out of all 1,300 species of these flappy mammals, there are few species more adorable than the Ussurian tube-nosed bat (Murina ussuriensisa) and their delightfully unique approach to surviving the harsh winters of East Asia.

A new study, published in the journal Scientific Reports, has discovered this small species of Vesper bat – they only weigh around 4.5 grams (0.16 ounces) – dig little holes in the snow and create tiny igloos in order to hibernate over the winter months. Until this discovery, scientists thought that the only mammals to hibernate in the snow were polar bears*.

However, like all good discoveries, it didn’t come easy. Hirofumi Hirakawa and Yu Nagasaka, two wildlife biologists from Japan, first heard rumors about this behavior in 2005. They talked to many of the scientists who had collected these accounts but there was not much in the way of hard evidence to back it.

From 2013 onwards, they headed out on a series of targeted searches around the woodlands of Sapporo, the mountainous northern Japanese island of Hokkaido. Over the course of 300 hours, they observed 37 individual bats exhibit this unexpected napping technique. In one case, in December 2017, Nagasaka noted how one bat was hiding in a snow-covered 6-centimeter-deep (2 inches) den. As spring broke in April 2018, he observed a bat emerge from this precise location and fly away.

Please enjoy this unbearably cute footage of a shivering Ussurian tube-nosed bat as it exits its snow den for the spring: 

The researchers concede that they were unable to see how long the bats had been in their little snowy dens, so they can not categorically say they were hibernating. Nevertheless, they believe their data and observations certainly points that way.

As you can imagine, laying in the snow for a couple of months is a risky business for a tiny mammal. The researchers found at least one bat that had died during its snow-capped hibernation.

Nevertheless, hibernating in snow does have some advantages. First of all, it's safe from predators and helps to bat to stave off dehydration upon waking. Snow provides also a surprisingly stable temperature. Although most species of bats tend to maintain a relatively high body temperature – about 30°C (86°F) – during hibernation, the researchers suggest that the tube-nosed bat might drop its body down to an extremely low temperature, as it’s too small to metabolically maintain any serious body heat. Its body fluids don’t freeze up by entering a state called “supercooling”. A handful of other bat species are known to be able to pull off this unusual feat, such as the Eastern red bat (L. borealis), which hibernates in leaf litter but can temporarily be buried by snow and frost.

*Technically polar bears don't hibernate, though it is the scientific term for when pregnant females build snow caves to wait out the months until birth in what is called "carnivore lethargy".

[H/T: National Geographic]

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