Shrinking the Brain During the Winter?
Every animal has its own way of getting through the winter months. One spends a long time hibernating, while another one ... shrinks. This is what wood shrews do. Various things become smaller during the winter, including their heads and brains.
For many species, a long, hard winter is a time when they consume more energy but cannot find as much food. Forest shrews have found a rather "shrewd" way of coping with this: they appear to reduce their energy consumption by shrinking their heads.
The Dehnel phenomenon
The fact that the skulls of shrews are smaller in winter than in summer was first described by Polish zoologist August Dehnel. He noticed this phenomenon in dead shrews that had died at different times of the year.
Several years ago, scientists at the Max Planck Institute in Germany decided to investigate the "Dehnel phenomenon" in live shrews as well. They caught some young wood shrews during the summer, chipped them and took X-rays of them. In the subsequent months, the shrews were regularly recaptured and measured. And yes, the size of their heads fluctuated across the seasons: they were larger in summer, shrank in winter and expanded again in spring.
Special trick
How do these animals manage to shrink their skulls? The skull is made up of several cranial bones. The X-rays suggest that the tissue in the sutures between these bones disappears as winter approaches, then grows back in the spring. Although the skull bone regenerates, the skull never quite returns to its original size.
Not only their heads
Through this research, the Dehnel phenomenon was not only demonstrated in living shrews, but it was linked to other biological changes as well. The shrews’ spinal columns also became shorter in winter, and organs such as the heart, lungs and spleen became smaller too. As the animals’ heads shrank, so did their brains: these became 20 to 30 percent smaller.
Less volume, less food
The researchers suspect that this is a survival mechanism. Shrews have a very high metabolic rate and do not hibernate or migrate in colder weather. This means they have to find another way to survive when food is scarce in the winter. Reducing their body weight is thought to lower their energy consumption and nutritional requirements, which could increase their chances of survival.