Japanese shrews sprout larger noses in winter while their brains shrink
Researchers found that long-clawed shrews in Japan develop noticeably bigger snouts during winter, even as their braincase contracts.
Analysis of 136 skulls of the long-clawed shrew (Sorex unguiculatus) collected on Hokkaido between 1948 and 1988 showed that, while the braincase shrinks in winter as part of Dehnel’s phenomenon, the animals’ snouts grow about 2.4 mm taller and 2.2 mm wider. Lead author Yugo Ikeda of Toyo University described the finding as a “reverse Dehnel’s phenomenon,” unexpected for a species already known to reduce body size in cold seasons.
He suggested that a larger nasal cavity could warm frigid air before it reaches the reduced brain or boost odor detection to locate scarce food under snow. Evolutionary ecologist Jan R. E. Taylor noted the need to test whether similar nasal changes occur in milder parts of the shrew’s range. Future work will aim to monitor live shrews to clarify the physiological benefits of this seasonal nasal expansion.
Why it matters
The discovery reveals a novel adaptation that could reshape how scientists view seasonal body changes in small mammals.
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