By comparing variations in the colour of the coats of the eastern grey squirrel (Sciurus carolinensis) in Montreal city parks, researchers found that hyper-local conditions appear to play a bigger role in determining wildlife traits than had been thought.
Despite its name, the eastern grey squirrel can sometimes have a black coat. The researchers found that squirrel coat colours across the Montreal region are shaped not only by urbanization, but also by such factors as forest canopy cover and the presence of the St. Lawrence River and its tributaries, which can limit movement and result in the creation of distinct populations.
"I visited almost 200 parks around the city on my bicycle during my free time the first summer that I was at McGill, and observed over 800 squirrels, some of whom were grey and others were black," said Francis Quang-Hai Dinh, the first author of the study, who was an undergraduate student at McGill when he collected information about the squirrels. Data was also gathered through park surveys with citizen science observations.
Squirrels with grey coats tend to be seen most frequently in Montreal. However, the researchers found that, even if grey coats always predominated, the proportion of black (melanic) squirrels was highest in areas of the city with cooler winter temperatures and greater forest canopy cover, where the heat-retention advantages of their darker coats may have offered a biological advantage in cooler winter weather. Contrary to patterns found in many cities, the prevalence of black-coloured squirrels in Montreal was generally lower in more urbanized areas. This interesting result will require future examination, the researchers said.
The findings highlight how wildlife can respond to environmental conditions at a very local scale, showing that cities are not uniform habitats but complex landscapes where differences between neighbourhoods, as well as geographic features such as rivers, can influence how animals adapt and evolve over time, the researchers said.
"People often think of cities as a single type of environment, but our findings show that the conditions animals experience can vary dramatically from one neighbourhood to another," said Allison Roth, the study's senior author, who was a GRIL postdoctoral fellow in McGill's Department of Biology during the time of data collection. Roth is now an Assistant Professor at the University of Missouri. "These local differences, along with barriers such as rivers, can shape how wildlife populations evolve, which means we need to look beyond simple urban-rural comparisons to understand adaptation in cities."
The study has just been included in a special feature published by five ecology journals whose focus is on how researchers are using large, open-access datasets and collaborative approaches to tackle big ecological questions.
"This project shows how discoveries can be accessible and that you can do science in your backyard," said Francis Quang-Hai Dinh.
About the study
"Fine-scale spatial variation in eastern grey squirrel melanism across a complex urban landscape," by Francis Quang-Hai Dinh, Isabella C. Richmond, Andrew P. Hendry, Allison M. Roth was published in Journal of Animal Ecology.
