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Bats Using Snow Dens Observed for the First Time

Researchers in Japan have discovered an extraordinary behaviour that has never been observed in bats until now. After thirteen years of research, scientists have finally concluded that the Ussurian tube-nosed bat (Murina ussuriensis) forms little ‘snow caves’ to make it through the harsh winters.

A unique bat behaviour

When temperatures drop during autumn, the bats will go to the ground to find a pile of snow. They will then make small indentations, and will wait there until snowfall covers the rest of their bodies. They will reside in these snow cavities for months, keeping warm on their body heat – effectively creating a tiny igloo. One bat in the study hibernated in its snow den from December 2017 to the middle of April 2018!

Polar bears are the only other mammals that exhibit this strange behaviour. Unlike bears, bats lack thick fur and insulating fat layers. This means that hibernating in the snow requires a lot of regulation. Their heartbeat and breathing must be slowed, and their internal temperatures need to be kept higher than the snow surrounding them. This requires little energy, and allows the bats to survive in freezing environments.

Sequence of images of an Ussurian tube nosed bat curled up in someone's hand and in a snow cave

Credit: Eiichi Kawashima (a,c), Akihiro Kawamura (b,e), Yushi and Keiko Osawa (d), and Yu Nagasaka (f).

Why build snow dens?

So why do these bats wait in the snow for so long? Hirofumi Hirakawa and Yu Nagasaka, the authors of the study, believe that the bats hibernate in this way for several reasons. They suggest that snow dens are a good shelter from predators and they keep their body temperatures stable. They also provide a continuous source of water over the winter months (the bats lick their snow den walls to stay hydrated).

To see the bats in their snow dens, click the video below:

Written by Caleb Compton (bat project volunteer)

Sources:
Evidence for Ussurian tube-nosed bats (Murina ussuriensis) hibernating in snow
These Bats Make Tiny Igloos to Survive the Winter

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