Shrews have a bonkers and heretofore undiscovered ability that Gizmodo states sounds like "some cruel, recurring witch's curse" but that scientists say is most likely a survival mechanism. According to a study published Monday in Current Biology, the wild common shrew shrinks its skull—by up to 20%—during the winter before regrowing it in the spring. And that's not all. Nature reports shrews also shrink other parts of their bodies, including their spine, heart, lungs, and spleen. Their brain mass drops by 20% to 30%, and overall body mass can shrink by more than 17% during the winter, according to the Guardian. As Gizmodo puts it, it's "obviously awesome and weird as hell."
Scientists had noted the discrepancy in shrew head size between winter and summer as far back as the early 1900s, but the common explanation was that large-headed shrews were simply dying off in the winter. The real reason appears to be much stranger. Researchers caught, X-rayed, tagged, and released numerous German shrews, which live 14 months or so on average. They ended up recapturing and X-raying 12 shrews in three key seasons. They found the skulls, brains, and bodies of those shrews actually shrank and regrew depending on the season. This could be a way to conserve energy when food is scarce as "the brain is energetically so expensive," biologist Javier Lazaro says. Researchers now hope to discover if wintertime shrews are cognitively impaired compared to their summertime selves. (Meanwhile, the brains in Spain are small because of rain.)