08/31/2026
Ever wanted to know why we have so many black squirrels !!!
Why the Great Lakes Region Has So Many Black Squirrels
Scurrying across through the snow-covered trees of Michigan and southern Ontario, the jet-black morph of the Eastern Gray Squirrel (Sciurus carolinensis) is a striking sight. Current evidence suggests that the melanistic (black) morph of this species is more common in Michigan and southern Ontario than anywhere else in North America 1 2. What could possibly explain such a pattern?
Melanistic Morphs and Natural Selection
As I discussed in my video Where is Black an Advantage? The Geography of Melanistic Animals , melanistic morphs are common in nature, and are often found with far greater frequency in certain habitats. Melanistic leopards, for instance, are far more common in densely forested habitats—more common than random mutation would explain 3. This suggests that natural selection has played some role in maintaining such a frequency. Melanism may have some advantages and disadvantages 4, and the advantages in dense forest may shift the balance in favor of melanism. Keep in mind that evolution is, by definition, the change in allele frequency of a population—we don’t need to see a perfect 1:1 relationship between leopard coat color and habitat in order to suggest that natural selection is playing a role.
An alternative explanation for non-random distributions of melanism is the founder effect. Let’s say a lizard species on the mainland is 95% green and 5% black. If 5 of the 10 individuals who happen to reach an island are black, the subsequent island generations will be black far more often than those of the mainland. The culprit here is just chance, not natural selection. But explanations like this fit poorly with the leopard example—there are no barriers between humid northeast India and the dry northwest…yet leopards are far more likely to be melanistic in the northeastern forests, and they are entirely absent in the northwestern desert 3 .
Does natural selection maintain the pattern in squirrel coat color we see in the USA? If so, how?
Black Squirrels in the Great Lakes Region
The Eastern Gray Squirrel inhabits deciduous and mixed conifer-deciduous forests in eastern North America. Its normal coloration is gray, like the bark of the trees it climbs. Interestingly, it does not hibernate.
And that lack of hibernation may be key to explaining this pattern. On a cold winter day, black fur may help a squirrel gain more heat from the sun. The squirrel would then need less energy to remain active on a winter day 5. The Great Lakes region is about as far north as the Eastern Gray Squirrel is found—farther north, the American Red Squirrel inhabits conifer forests of the Canadian Taiga.
But if that’s the case, why don’t we see just as many black squirrels in Wisconsin, or Maine? Why would they be more common in a specific area around the Great Lakes?
Well, studies have shown that black fur has the strongest thermal advantage on cold, cloudy days. The difference in heat gain between gray and black fur is greatest in cold and cloudy conditions 5 .
As you can see in these average cloud cover maps for November, December, January, and February, the areas downwind of the Great Lakes in winter are far more cloudy than surrounding forest regions. In winter, cold continental air masses blow from the north, west, or northwest across the region. When they cross the relatively warm lakes, they pick up a tremendous amount of water v***r, leading to cloudy conditions along with snow or rain. This may be why you’re far more likely to see a black squirrel in Michigan, northern Ohio, or southern Ontario rather than Wisconsin.
As the field of conservation biology continues to use genetics to better understand our world, we will surely learn more about the past, present, and future of black squirrels in the Great Lakes region. Regardless of the evolutionary processes that brought them about, they certainly add a flicker of life to a dreary winter day.
