Black squirrels are a striking variation of a common sight in many parks and woodlands. These dark-furred animals are not a separate species but rather a melanistic subgroup, primarily of the Eastern gray squirrel (Sciurus carolinensis) and, less frequently, the fox squirrel (Sciurus niger). Their deep, dark coloration sets them apart. This unique appearance is a result of a genetic variation within their species.
Global Geographic Presence
Black squirrels are found across various regions, with a notable presence in North America. They are particularly common in the northern portions of the Eastern gray squirrel’s range, especially around the Great Lakes Basin. Significant populations thrive in the Canadian province of Ontario, where they often form the majority of the squirrel population. In the United States, large numbers are found in Michigan, Ohio, New York, and Pennsylvania, as well as Illinois, Indiana, and Maryland.
Beyond North America, black squirrels have established themselves in the United Kingdom. Their presence originated from black morphs imported from North America, likely escaping from private collections or zoos in the early 20th century. The first recorded wild black squirrel sighting in the UK was in Woburn, Bedfordshire, around 1912. Today, they are most commonly observed in counties like Hertfordshire, Bedfordshire, and Cambridgeshire in southeastern England.
The Science Behind Their Dark Fur
The black fur of these squirrels is due to a genetic condition called melanism. Melanism results from a genetic mutation that causes an overproduction of melanin, the pigment responsible for dark coloration in skin and fur. In Eastern gray squirrels, this phenomenon is linked to a specific variant pigment gene, the melanocortin 1 receptor (MC1R) gene, which has a 24 base-pair deletion. This allele, MC1R∆24, increases dark pigment production.
The gene responsible for melanism in Eastern gray squirrels is considered semi-dominant. A squirrel inheriting one copy of the melanism gene and one normal gene can exhibit a brownish-black coat, while those with two copies of the mutant gene tend to be jet black. Research indicates this variant pigment gene likely originated in the fox squirrel and was transferred to Eastern gray squirrels through interspecies mating.
Why They Thrive in Specific Locations
The prevalence of black squirrels in certain areas is influenced by historical factors, their adaptability to urban environments, and potential adaptive advantages. Many existing populations in the United States, such as those in Kent, Ohio, and Battle Creek, Michigan, were established or augmented through deliberate reintroductions. For example, Kent State University released ten black squirrels from London, Ontario, onto its campus in 1961 to reintroduce the morph to Ohio. Similarly, in the late 1940s, black squirrels from Michigan were released in Stanley Park in Westfield, Massachusetts, leading to their spread in the Pioneer Valley.
Black squirrels often thrive in urban environments, which provide reduced predation pressure and abundant, accessible food sources from human activity. Their comfort around humans allows them to exploit resources like parks, backyards, and garbage bins. Urban settings may also offer refuge from hunting pressures, which disproportionately affect squirrels in rural areas.
Theories suggest adaptive advantages for black fur, particularly in colder climates. Darker coloration may allow black squirrels to absorb and retain more heat from sunlight, providing a thermal benefit during harsh winters. This thermal advantage could contribute to their higher frequency in northern regions. While some studies suggest black fur may offer better camouflage in dense, shaded old-growth forests, other research indicates gray squirrels might be less conspicuous in today’s secondary forests.