Black squirrels, with their distinctive dark fur, often spark curiosity about their origins. Their striking appearance frequently leads people to wonder if they represent a separate species.
A Color Variation, Not a Distinct Species
Black squirrels are not a separate species but are a melanistic form of the Eastern Gray Squirrel (Sciurus carolinensis). This means they possess an excess of dark pigment, melanin, in their fur, skin, or feathers, which is the opposite of albinism. Despite their different coloration, black squirrels are genetically the same as gray squirrels and can interbreed with them, producing offspring of either color. Melanism is a natural genetic variation observed in several squirrel species, though it is most common in Eastern Gray Squirrels and Fox Squirrels (Sciurus niger).
The presence of black fur in these squirrels is simply a color morph. Black squirrels carry either one or two copies of a black pigment gene. A squirrel with two copies of the black gene will be jet black, while one with one black and one gray gene will appear brown-black.
The Genetics Behind Their Dark Coats
The dark coloration in black squirrels results from a specific genetic mutation. This mutation occurs in the melanocortin 1 receptor (MC1R) gene, which plays a central role in regulating the production of melanin. Specifically, a 24 base-pair deletion in the MC1R gene leads to an overproduction of eumelanin, the dark pigment, resulting in their characteristic black fur. This genetic change essentially keeps the pigment production switch “on,” leading to continuous dark melanin deposition.
The allele responsible for the black fur is referred to as MC1R∆24. Research suggests that this specific variant originated in fox squirrels and was later passed to Eastern Gray Squirrels through interspecies mating. Although the black gene is considered incompletely dominant, meaning that heterozygotes (with one black and one gray allele) can be brown-black, and homozygotes (with two black alleles) are jet black, the gray type is genetically recessive. This genetic mechanism explains the range of dark shades seen in black squirrels.
Where Black Squirrels Are Found
Black squirrels share the same natural range as Eastern Gray Squirrels across North America. They are most frequently observed in the northern parts of this range, particularly around the Great Lakes Basin. Ontario, Canada, and Michigan boast the highest concentrations of black squirrels, where they can even be the predominant color morph. For example, black morphs account for approximately 66% of squirrels in Ontario and 56% in Michigan.
Beyond these areas, significant populations are found in other regions surrounding the Great Lakes, with about 15% of Eastern Gray Squirrels in those states being melanistic. Scattered populations also exist across the eastern United States, including states like New York, Ohio, Maryland, Indiana, Virginia, Washington, D.C., Iowa, Wisconsin, Minnesota, and Pennsylvania. Some populations, like those in Washington, D.C., and Kent, Ohio, originated from reintroduction programs where black squirrels were purposefully released. The prevalence of black squirrels can also be higher in urban environments compared to rural or forested areas.