- While black is a naturally occurring variation in coat color, black (also known as melanistic) eastern gray squirrels get more common in northern parts of the range, especially in the eastern Great Lakes region.
- Scientists think that their black fur may make them better at thermoregulating during Michigan’s cold and cloudy winters.
- Some research suggests the black coat color may also help the squirrels avoid getting hit by cars in more urban areas.
Squirrels might be one of the least exotic animals. They’re everywhere–from state parks to city centers. Forty-nine of the 50 states have least one native squirrel species. Michigan alone has nine! But it was one type of squirrel in particular that piqued listener Jonathan DeKoekkoek’s interest. He sent this question to the On Hand team:
Why is it that it seems like Michigan is one of the only states to have a large population of these black colored squirrels?
First things first: if you are looking at a black squirrel in Michigan, you are probably looking at an eastern gray squirrel. Black is just one of the naturally occurring coat color variants in this species. While Michigan is definitely not the only state where you can find the black morph of the eastern gray, research does suggest that they are a lot more common here than in many other states in the species’ range.
A 2022 study looked at the distribution of the black morph of eastern gray squirrels across 43 North American cities. Detroit ranked second, behind Ottawa and just ahead of Toronto.
Hobart and William Smith Colleges biology professor Brad Consentino was one of the researchers behind that 2022 study. He’s also a lead scientist for a project called SquirrelMapper, which uses citizen science data to help biologists understand how humans are impacting wildlife evolution.
"We study how cities and the environmental change in cities cause wildlife to evolve in different ways, and so squirrels are a great species for that kind of question,” Consentino said. “People know squirrels. They're active during the day, they're highly visible. And they come in these different coat color morphs that has a genetic basis, which is good for studying evolutionary processes that kind of cause how they change over time."
What makes black squirrels particularly interesting to researchers like Consentino is that eastern gray squirrels' coat color varies so widely across the range. The proportion of the eastern gray squirrel population with with melanistic (black) fur increases as you move north.
Researchers have a couple theories about why that might be the case. The first is that black fur might give squirrels an edge when it comes to keeping themselves warm. Studies in a related species–the fox squirrel–found that advantage was particularly pronounced on cloudy days.
“If you look at how fast black versus the more typical gray morph heats up on cloudy days, the black morph heats up faster," Consentino explained. "And so if you think about like where's cloud cover? It's super cloudy in the Great Lakes, right?”
Black squirrels may also be more visible to humans in both rural and urban settings. While their visibility in forests may have contributed to overhunting after European colonization, it might be an asset in urban environments.
Consentino was part of a study that looked at the color of road-killed squirrels on a 90-mile stretch of road in Syracuse, NY. They found that black squirrels were underrepresented in comparison to their population by about 30%.
“But the curious thing is, is black squirrels, even though they get that benefit, they are not abundant in every city. So if you go from town to town, from Kalamazoo, to Grand Rapids, to Detroit, you'll definitely find variation in in the frequency of black squirrels.”
How squirrels got to those cities in the first place might be a good clue about why the population of black squirrels varies so much by locality. When humans were building cities, they were also cutting down the trees which squirrels depended on for food and shelter. When cities began to incorporate more trees and green spaces, they also re-introduced squirrels to beautify those landscapes.
“And the most famous case I should mention is in Washington, D.C.. So Teddy Roosevelt actually struck a trade deal with Canada and had black squirrels imported to Washington, D.C.. They were introduced to the National Zoo, and since then they've expanded, so they've become 30 [to] 35% of the population. In Washington, D.C. there were never any black squirrels before that introduction.”
You can help scientists like Brad Consentino understand how the black squirrel population in Michigan is changing! If you want to contribute to SquirrelMapper by documenting the squirrels in your neighborhood, find out how to do that here.
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