Wildlife

Mice are Shrinking

According to a well-studied but controversial principle known as Bergmann’s Rule, species tend to be larger in cold climates and smaller in warm ones. As human impacts heat the planet, will animals shrink over time?

To test this, a new study, published today in Scientific Reports, analyzed 70 years of records of the North American deer mouse, Peromyscus maniculatus, one of the most common mammals in the U.S. and the best-documented rodent in North American museum collections and surveys.

Unexpectedly, researchers found deer mice are generally decreasing in mass over time, but this trend may not be linked to changes in climate or human population density, a proxy for urbanization. In another surprise finding, larger-bodied deer mouse populations are getting smaller and smaller-bodied populations are getting larger.

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