Shrews Grow Bigger Snouts in Winter for Cold Survival 2026

Shrews grow bigger snouts in winter to survive cold air, a fascinating adaptation known as the reverse Dehnel's phenomenon. Researchers have uncovered that long-clawed shrews (Sorex unguiculatus) actually enlarge their rostrum—the snout area—during the coldest months, while other body parts shrink. This counterintuitive change helps them cope with frigid temperatures and is a remarkable example of seasonal plasticity in mammals.

What Is Dehnel's Phenomenon?

Dehnel's phenomenon describes the seasonal shrinking of body mass, skull size, and brain mass in certain small mammals like the common shrew and European mole. This reduction lowers energy demands when food is scarce. However, the long-clawed shrew flips this pattern for its snout, showing a reverse Dehnel's phenomenon where the rostrum actually grows larger in winter.

The Reverse Dehnel's Phenomenon in Long-Clawed Shrews

Scientists from Toyo University in Japan examined 136 skulls of long-clawed shrews collected in Hokkaido between 1948 and 1988. By tracking 16 measurements month by month, they found that winter-collected shrews had a brain case height 12% smaller than younger shrews from late summer, but their snout height increased by 7% and width by 6%. This physical alteration of the bone structure suggests a true morphological change, not just swelling.

Why would a shrew need a larger snout in winter? The researchers hypothesize that a bigger rostrum may enhance the surface area for sensory receptors, improving the ability to detect prey under snow or in colder conditions. Alternatively, it could help warm the air before it reaches the lungs, reducing heat loss. The exact function remains under investigation, but the pattern is clear.

Implications for Climate Adaptation

This discovery adds to our understanding of how small mammals adapt to seasonal environmental stress. As climate change alters winter conditions, such morphological flexibility could be crucial for survival. The long-clawed shrew's ability to reversibly modify its skull structure offers a model for studying rapid evolutionary responses.

• Seasonal plasticity allows shrews to optimize energy use without permanent anatomical changes.
• The reverse Dehnel's phenomenon is unique to the snout, highlighting region-specific adaptations.
• Skull measurements from museum specimens provide valuable long-term data for climate research.
• Understanding these mechanisms may inform conservation strategies for small mammals facing habitat changes.

Key Takeaways

The long-clawed shrew's winter snout growth is a striking example of nature's ingenuity. While most of the body shrinks to save energy, the snout expands—possibly to enhance sensory perception or respiratory efficiency. This research underscores the complexity of seasonal adaptations and the importance of preserving biodiversity.

FAQ

This research, published in Proceedings of the Royal Society B, opens new avenues for studying how mammals adapt to extreme environments. As winters become more unpredictable, such insights are invaluable for predicting species resilience.

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