Shrews shrink their own skulls to survive the winter

October 25, 2017, 6:31 a.m.
A common shrew sitting on a mossy rock
Photo: Erni/Shutterstock

When we think about mammals getting ready for winter, our minds turn to last-minute foraging and long periods of hibernation. The notion of critters shrinking their own skulls doesn't enter our minds, but it should, at least in the case of the wild common shrew (Sorex araneus).

A study published in Current Biology tracked the skull sizes of 12 common shrews caught in Germany between June 2014 and October 2015. In the summer months, the shrew's skull — not to mention organs, like the heart and lungs — was the expected size. During winter months, the researchers found that the skull and organs all shrank a great deal; even the brain mass dropped between 20 and 30 percent. Come spring, however, the sizes of things began to slowly return to normal. Well, normal-ish. The skulls didn't return to their exact pre-winter shapes from the following summer.

"We hypothesize that these seasonal changes could have adaptive value," Javier Lázaro, a biologist at the Max Planck Institute for Ornithology in Radolfzell, Germany, explained to Nature.

Those "adaptive values" include needing to forage for less food. By reducing their overall body mass, the shrews require less food to make it through the winter. This ability, according to Lázaro, may be present in other small mammals with high metabolisms that don't engage in typical mammalian winter habits.

Perhaps these tiny shrews have big things to teach us about our own bodies. As the researchers note at the end of their study, "Our results show the extraordinary extent to which the postnatal mammalian skeleton can maintain flexibility if the proper genetic programs are activated. This opens new and important avenues in understanding how certain degenerative processes can potentially be reversed in the skeleton and other tissues."

Related on MNN: 11 of the smallest mammals in the world