Black squirrels do inhabit Illinois, though they remain a relatively uncommon sight across the state’s total squirrel population. These striking animals are not a separate species but represent a color variation of the widespread Eastern Gray Squirrel, Sciurus carolinensis. Their dark fur is the result of a natural genetic phenomenon.
Understanding Melanism in Squirrels
The deep, dark color of a black squirrel is the result of a genetic trait known as melanism, which is the opposite of albinism. This condition is caused by a specific mutation in the melanocortin 1 receptor (MC1R) gene that leads to an overproduction of the dark pigment called eumelanin. Research has identified this mutation as a 24-base pair deletion in the Sciurus carolinensis gene, which is responsible for regulating color production.
Black squirrels are considered a color morph of the Eastern Gray Squirrel. The deletion allele responsible for the black color is incompletely dominant. A squirrel with one copy of the gene deletion may appear brownish-black, while those with two copies often display the jet-black phenotype.
Confirmed Distribution and Habitats in Illinois
Black squirrels are concentrated in specific, often urbanized, regions within Illinois, particularly in the northern counties around the Great Lakes Basin. In the Chicago metropolitan area, sustained populations have been observed on university campuses, including the University of Chicago in Hyde Park and Loyola University in Rogers Park. They are also frequently spotted in suburban areas like Schaumburg, Downers Grove, and South Barrington.
Outside of the Chicago area, localized hotspots exist across the state, often in smaller cities and towns. For instance, populations are known in central Illinois communities like Fisher and Gibson City, as well as around the Peoria area. The Augustana College campus in the Quad Cities is another noted location where the black morph is a common sight. These animals thrive in urban and suburban environments due to the consistent food sources and fewer natural predators found in city parks and residential neighborhoods.
Historical Introduction of Black Squirrel Populations
The concentrated black squirrel populations in Illinois are largely a result of both natural expansion and intentional introductions. The species’ black morph historically occurs more frequently toward the northern limits of the Eastern Gray Squirrel’s range, which includes the Great Lakes region. This proximity to states like Michigan and the Canadian province of Ontario, where black squirrels are the predominant color, has contributed to their presence in northern Illinois.
More localized populations are often linked to specific human-led efforts of translocation in the late 19th and early 20th centuries. The Quad Cities area, for example, has a unique local history suggesting the black squirrels originated from a pair released on Rock Island Arsenal. This release was reportedly carried out by D.D. Palmer, the founder of Palmer College of Chiropractic, after a grateful patient gifted him the animals. Such deliberate introductions helped establish the black squirrels in various isolated pockets across Illinois, where they have since thrived and slowly expanded their local range.