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Francis Quang-Hai Dinh’s first summer at McGill University was spent on his bicycle, searching for squirrels across Montreal-area parks.
He pedalled to nearly 200 green spaces — from Mirabel to Saint-Bruno — observing and recording more than 800 grey and black squirrels.
What started as an undergraduate task quickly turned into a passion project to uncover how the city’s layout and winding waterways are quietly driving evolution.
“I fell in love with them after I had started staring at them for long enough and just giving them enough thought,” said Dinh. “We don’t even think of squirrels as being animals. They’re practically just pests, but they are indeed wildlife.”
Without a car and facing limited public transit options in suburban areas, Dinh relied on his bicycle to travel as far as possible, making him the only known researcher to manually survey squirrels park-by-park across the region.
Why black squirrels are more common up north
He found on average, about 12 per cent of squirrels in Montreal are black. But the further north he went, the more black squirrels there were.
In areas just north of Laval, he found up to 40 per cent of squirrels were black — a term used to describe varying, darker coats on squirrels that aren’t the common grey.
On the island of Laval, about 20 per cent were black. On the island of Montreal, around 15. And on the south shore of Montreal, the percentage dropped to just two or three per cent, said Dinh, who is now studying integrative biology at the University of Illinois Urbana-Champaign.
The study found three main reasons for this, and the No. 1 is temperature. The further north, the cooler it is, hence more black squirrels.
“Because their black coloration can absorb better heat than the greys,” he said.
But it’s also connected to forest cover: denser tree canopy creates a darker backdrop, where black squirrels are better camouflaged.
Squirrels are an evolutionary change model
The study’s senior author, Allison Roth, is an assistant professor at the University of Missouri and a former McGill postdoctoral fellow. She said the research is less about squirrels themselves and more about using them as a model to test how urban environments drive evolutionary changes.
According to Roth, cities are far from uniform. Their diverse neighbourhoods, varying levels of tree cover and distinct boundaries — like Montreal’s waterways — create fine-scale environmental variations that can lead to different genetic and physical adaptations within the same animal population.
“One really important thing about Montreal that you don’t get in many other cities across North America is that it’s highly segmented by the St. Lawrence River and its tributaries,” said Roth.
A new McGill study found that eastern grey squirrels in the city vary in coat colour depending on the neighbourhood they live in. The animals are influenced by local environmental conditions, including temperature and forest cover.
“So it almost creates these distinct little islands, and we might see different patterns of squirrel melanism depending on: are these guys able to cross rivers, or are they really potentially being isolated on these land islands?”
All this is “really important for understanding how this evolution might occur,” she explained.
Cities are just part of the puzzle
The study, Fine-scale spatial variation in eastern grey squirrel melanism across a complex urban landscape, can be found online.
While most previous studies on how city animals evolve have only compared cities as a whole to the countryside, this one narrowed down changes in wildlife on a neighbourhood-by-neighbourhood basis.
While scientists used to think human development was the main force driving these changes, the study shows that cities are just part of the puzzle. Urban sprawl changes the local temperature and cuts down tree cover, while riverways create natural barriers.
“Urbanization does not directly predict melanism once local vegetation structure and winter microclimate are accounted for, but instead influences melanism indirectly through these environmental mediators,” the study finds.
The research is being published as part of a special feature by five ecology journals looking at how researchers use data and collaboration to tackle big ecological questions.
As for Dinh, he said he can’t look at wildlife the same way anymore.
“We have this kind of dichotomy that city and nature are two completely separate things. And yet the reality is wildlife will continue to live and to persist despite whatever modifications we bring to it,” he said.
