Shrews shrink their heads during the winter, study reports

Posted on FEB 13, 2019

Researchers have found the mechanisms that allow the common shrew to shrink and regrow its head during different parts of the year,

Common shrews are able to shrink their head size during the winter in order to adapt when food is scarce, a new study published in Current Biology reports.

Researchers from the Max Planck Institute for Ornithology recorded this odd behavior after capturing and tagging different shrews across Germany.
The team tested the small mammals for both skull size and body mass over the winter. This revealed that, not only were their heads getting smaller, their spines got shorter, and several of their major organs shrank as well. Brain mass dropped between 20 and 30 percent in cold months and then regrew in spring.

While researchers are not sure, they believe this change occurs as a way to offset the shrew's fast metabolism. By reducing body mass in the winter, the mammals could likely raise their chances for survival in harsh conditions.

"We hypothesize that these seasonal changes could have adaptive value," said lead author Javier Lzaro,a biologist at the Max Planck Institute for Ornithology, according to Nature. "Reducing brain size might save energy, as the brain is energetically so expensive."

In addition to the analysis, scientists also fitted twelve shrews with a microchip that allowed them to monitor the animals' bodily changes.This showed that shrew skulls shrink by about 15 percent from summer to winter, an effect that is likely caused by the resorption of tissue at the joints between skull bones. Though the bone regenerates in spring, it does not quite return to its original size.

To follow up on the discovery, the team next plans to look at what brain structures change most from season to season. They also want to see if the mammals suffer any cognitive impairments during the winter and if there are other species that lose mass in a similar way.

Such processes could help shed light on a little known evolutionary mechanism and may largely improve our understanding of how different species change over time.

"We are dealing with a system that loses in this case bone tissues and, in some still unknown mechanism," said Lzaro, according to Newsweek. "They are able to regenerate this tissue."