Shrews Grow Bigger Snouts in Winter to Survive Cold Air 2026

Shrews grow bigger snouts in winter to survive cold air, according to new research that reveals a surprising twist on a known survival strategy. While many small mammals shrink their bodies and skulls during colder months, the long-clawed shrew (Sorex unguiculatus) does the opposite with its snout, expanding it to better cope with frigid temperatures. This finding, published in Proceedings of the Royal Society B, adds a new dimension to our understanding of how animals adapt to seasonal changes.

The Reverse Dehnel's Phenomenon

Scientists have long known about Dehnel's phenomenon, where certain small mammals like the common shrew and European mole reduce their body mass, skull size, and brain mass in winter to lower energy demands. However, the long-clawed shrew exhibits a reverse Dehnel's phenomenon in its snout, or rostrum. Instead of shrinking, the snout grows larger, likely to enhance the animal's ability to sense and capture prey in cold conditions.

Study Details

Researchers led by Dr. Yugo Ikeda from Toyo University in Japan examined 136 skulls of long-clawed shrews collected in Hokkaido between 1948 and 1988. These specimens, housed at the Botanical Garden of Hokkaido University, provided a rare opportunity to track seasonal changes without harming live animals. The team measured 16 skull features across different months, focusing on the brain case and the rostrum.

Key Findings

The study revealed that shrews collected from January to April had a brain case height 12% smaller than younger shrews from August to September. In contrast, the snout height was 7% larger and its width 6% greater in winter-collected shrews. This indicates a true physical change in bone structure, not just tissue swelling.

Implications for Understanding Adaptation

This discovery challenges the assumption that Dehnel's phenomenon applies uniformly across all body parts. The long-clawed shrew's enlarged snout likely improves its olfactory and tactile senses, helping it find food under snow or in tight burrows. The study also highlights the importance of museum collections in revealing long-term ecological patterns.

Key Takeaways

• Long-clawed shrews grow larger snouts in winter, a reverse of Dehnel's phenomenon.
• Brain case shrinks by 12% while snout height and width increase by 7% and 6%, respectively.
• This adaptation may enhance sensory perception for foraging in cold environments.
• Museum specimens are invaluable for studying seasonal morphological changes.

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