It may sound strange, but the average size of mice has been shrinking. A new study from Scientific Reports shows that the average mass of the North American deer mouse has been steadily declining over the last 70 years. This body size reduction is theorized to be linked to global temperature increases, including temperature rises in “urban heat islands.” This article will explore what this means overall.

Global Climate and Body Size of Mice

As global climate increases, the body size of the deer mice has been shown to shrink, according to this study. Overall, a fairly well-documented understanding that populations and species of warm-blooded animals are larger in colder environments, and smaller in warmer climates. This is referred to as Bergmann’s Rule. It is possible that as global climate change occurs, the deer mouse has gotten smaller.

Urban Heat Islands and Mice

An Urban Heat Island is the concept that urban areas are warmer than most of the surrounding areas. This is due to a number of factors. A few examples include heat reflecting off of the asphalt and buildings, the localization of a large number of people, an increased concentration of vehicles, as well as the concentration of smog from those vehicles. All of this together creates a temperature hotspot compared to the rest of the region. As urbanization reduces habitats while providing a concentration of food, many mice populations are active in urban areas. With warmer temperatures in urban areas overall, it would make sense for urban rodents to be smaller than those found elsewhere.

Habitat Fragmentation and Mouse Size

Habitat fragmentation is the division of ecosystems, into smaller, less secure ones. Generally, this refers to habitat breakdowns from human development. Urbanization, highway development, and agriculture are common causes of habitat fragmentation. As sections of an ecosystem are divided, it becomes harder for the habitat to sustain larger animals and larger populations of them. Food scarcity and shrinking borders may leave animals struggling with limited resources. This can also lead to a more diminutive population of a species.

What Smaller Mice Mean to Your Home

So what does this all mean? As mice are shrinking in size, this means that they may be more equipped to hide out in your home or commercial property. Mice can generally squeeze through tight cracks and holes, but a smaller mouse could breach an even tighter space. A smaller mouse population could, in theory, access your home more easily.

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