Black squirrels exist as a color variation within common squirrel species, primarily the Eastern Gray Squirrel. They are not a separate species but a melanistic form, meaning their dark fur results from a genetic difference affecting pigment production.
The Science Behind Their Color
The dark coloration in black squirrels results from melanism, a genetic condition causing an overproduction of melanin. Melanin is the pigment responsible for dark colors in fur, skin, and eyes. In Eastern Gray Squirrels (Sciurus carolinensis), this trait is often linked to a specific genetic mutation: a 24 base-pair deletion in the melanocortin 1 receptor (MC1R) gene, known as the MC1R∆24 allele. This variant allele is incompletely dominant. A squirrel with one copy of the black pigment gene and one gray gene will appear brown-black, while those with two copies will be jet black.
While the MC1R gene is a primary factor for melanism in Eastern Gray Squirrels, the genetic basis can differ in other species. For example, melanism in fox squirrels (Sciurus niger) may involve a variant pigment gene, sometimes originating from interbreeding with Eastern Gray Squirrels.
Where Black Squirrels Are Found
Black squirrels, primarily melanistic Eastern Gray Squirrels, are found throughout the natural range of their gray counterparts in North America. Their prevalence varies geographically, with higher frequencies observed in the northern portions of the Eastern Gray Squirrel’s range, especially around the Great Lakes Basin.
In Canada, black squirrels are abundant in Ontario, often constituting the majority of the Eastern Gray Squirrel population. In the United States, large populations exist in Michigan, Ohio, and parts of the Northeastern and Midwestern states, including Maryland, Indiana, and Pennsylvania. Black squirrels have also been introduced to other regions, such as the United Kingdom. Urban environments often show a higher frequency of black morphs compared to rural areas.
Black Squirrels and Their Gray Counterparts
Black squirrels are not a distinct species, but rather a color variant within species like the Eastern Gray Squirrel. This means they share the same fundamental behaviors, diets, and life cycles as their gray relatives. While their appearance differs, their classification remains the same.
Some research has explored whether the black fur confers any ecological advantages or disadvantages. The darker fur absorbs more solar radiation, which can provide a thermal advantage in colder climates, helping them retain body heat. This thermal benefit may have contributed to their ability to expand into more northern regions. Regarding camouflage, black squirrels might blend more effectively in dimly lit environments, such as dense old-growth forests or urban areas with shadows. Historically, black squirrels were more prevalent in the heavily forested landscapes of North America before extensive deforestation.
Behavioral studies generally show no significant differences in aggression or wariness between black and gray morphs. Although some anecdotal observations and older studies suggested black squirrels might be more aggressive, potentially due to higher testosterone levels, more recent research has not consistently supported this claim. Aggressive behaviors in squirrels are typically influenced more by environmental factors, such as competition for food or mating season, rather than fur color.