Cities Change Animal Anatomy

Research led by scientists from Drexel University and University of Michigan reported in a yet-to-be published paper that urbanisation contributes to different body sizes and cranial shapes in urban and rural house mice. 

As cities grow larger, it becomes important to understand the effect of urbanisation on animals from a public health and environmental perspective. Mice are one of the most common animals in cities and are carriers of several diseases such as Hantavirus and Salmonellosis, which can easily be passed on to humans. Furthermore, the knowledge of mice anatomy in large cities may even serve as vital indicators of underlying environmental changes. 

Stephen C. Kupchella, researcher from the Department of Biology at Drexel University, led the study to investigate how urbanisation contributes to intraspecific variations in mice. The team collected mice using live traps in New York, Philadelphia, and Richmond, as well as from neighbouring rural areas from the respective cities.  

As the authors point out, “the differences observed in this study could result from many factors” encompassing both genetic and environmental factors. However, it is nonetheless a strong foundation for further research to investigate the more specific elements that could affect the anatomy and physiology of house mice. 

The morphology of mice was measured broadly under three categories: weight, linear size, and cranial traits. The cranial traits were measured using Geometrics Morphometrics, which is a powerful 3D modelling tool that helps biologists understand anatomical structures. 

The team found strong evidence that urban mice were smaller in body size and body mass than rural mice. Changes in cranial size were mostly allometric, meaning that they were driven by differences in body size, although some variation independent of body sizes were also reported 

Cities create urban heat islands which significantly increase temperature, while impermeable surfaces disrupt the natural water cycle, increasing the risk of flooding. Together with the obvious increases in noise and air pollution, these factors can drastically change food availability in urban areas. As urban animals are typically underrepresented in museums, it is crucial to increase research and exposure on how urbanisation can alter animal behaviour or anatomy. 

By Kazuma Oura, July 19, 2026.

Edited by Marina Milsum.