Long-clawed shrews expand snouts in winter to survive cold

Researchers have identified a unique physiological adaptation in long-clawed shrews known as the “reverse Dehnel’s phenomenon.” While many small mammals undergo Dehnel’s phenomenon—a process where body mass, brain size, and skull dimensions shrink during winter to conserve energy—the long-clawed shrew exhibits a contradictory structural change.

A study published in Proceedings of the Royal Society B reveals that during winter, the shrews' snouts temporarily expand, increasing in height by 7% and width by 6%. This occurs even as other parts of the skull and the braincase shrink. Scientists theorize that this expanded nasal cavity may house an increased vascular network designed to warm freezing air before it reaches the brain.

Led by Dr. Yugo Ikeda of Toyo University, the team analyzed 136 museum-preserved skulls from Hokkaido, Japan, collected between 1948 and 1988. The morphological changes are reversible, with the skull structures returning to their larger sizes by late summer and autumn.