Black squirrels are a fascinating variation within common squirrel populations. Their unique appearance is a result of genetic factors.
The Genetics Behind Their Color
Black squirrels are a melanistic variation of the eastern gray squirrel, Sciurus carolinensis, and, less commonly, the fox squirrel, Sciurus niger. Melanism refers to an unusually high amount of dark pigment, eumelanin, which gives their fur its black coloration. This pigmentation stems from a specific genetic mutation.
In eastern gray squirrels, this mutation involves a 24 base pair deletion within the melanocortin 1 receptor (MC1R) gene, known as MC1R∆24. This genetic alteration causes the MC1R protein to be shorter, effectively instructing the melanocytes to continuously produce eumelanin. Research indicates this variant gene likely originated in black fox squirrels and was subsequently transferred to eastern gray squirrels through interspecies mating. The presence of one copy of this mutant gene can result in a brown-black coat, while two copies lead to a jet-black appearance.
Geographic Distribution and Population
Black squirrels are found predominantly across North America, particularly in the eastern United States and Canada. They are notably common within the Great Lakes Basin, with significant populations in Ontario, Canada, and Michigan, U.S. In these areas, black squirrels can constitute a majority of the local squirrel population, reaching frequencies of approximately 66% in Ontario and 56% in Michigan.
Beyond these key regions, populations of black squirrels also exist in states such as Ohio, Maryland, Indiana, Virginia, Washington D.C., Iowa, Wisconsin, Minnesota, and Pennsylvania. While their overall frequency can be relatively low in some areas, sometimes as rare as one in 10,000 eastern gray squirrels, their distribution is often concentrated in urban environments. This urban prevalence contrasts with historical patterns, where black squirrels may have been more widespread in dense, old-growth forests, where their dark fur provided camouflage.
Are They a Distinct Species?
Black squirrels are not a distinct species; they are a color morph within the existing eastern gray or fox squirrel populations. They are genetically identical to their gray or red counterparts, with the only difference being their fur coloration. They can readily interbreed with gray squirrels, producing offspring that can exhibit either black or gray fur.
The black coloration may provide certain advantages, such as enhanced thermoregulation in colder climates, where darker fur can absorb more solar radiation. In historical contexts, their dark coats offered better concealment in the dense, shaded environments of old-growth forests. Their ability to interbreed freely with other color variations confirms their status as members of the same species.