The black squirrel occurs as a "melanistic" subgroup of both the eastern gray squirrel and the fox squirrel. Their habitat extends throughout the Midwestern United States, in some areas of the Northeastern United States, eastern Canada, and also in the United Kingdom. The overall population of black squirrels is small when compared to that of the gray squirrel. The black fur color can occur naturally as a mutation in populations of gray squirrels, but it is rare. The rarity of the black squirrel has caused many people to admire them, and the black squirrels enjoy great affection in some places as mascots. In several U.S. states, as well as in Canada and the United Kingdom, black squirrels have been introduced into the wild in the hope of increasing their numbers.
As a rare mutation of both the eastern gray and fox squirrel, individual black squirrels can exist wherever gray or fox squirrels live. Among eastern squirrels, gray mating pairs cannot produce black offspring. Gray squirrels have two copies of a normal pigment gene and black squirrels have either one or two copies of a mutant pigment gene. If a black squirrel has two copies of the mutant gene it will be jet black. If it has one copy of a mutant gene and one normal gene it will be brown-black. In areas with high concentrations of black squirrels, litters of mixed-color individuals are common. The black subgroup seems to have been predominant throughout North America prior to the arrival of Europeans in the 16th century, when America's old growth forests were still abundant and thick. The black squirrel's dark color helped them hide in these very dense and shaded old growth forests. As time passed, extensive deforestation and the hunting of squirrels for their meat and pelts led to biological advantages for gray colored individuals; their light-gray color became advantageous in their newly changed habitat. Today, the black subgroup is particularly abundant in the northern part of the eastern gray squirrel's range. This is due to two main factors. Firstly, black squirrels have a considerably higher cold tolerance than that of gray squirrels. Secondly, because the northern forests are denser and thus darker, the black squirrel enjoys the advantage of better concealment among this dimly lit habitat.
Large natural populations of black (eastern gray) squirrels can be found throughout Ontario and in several parts of Ohio, Maryland, Michigan, Houston, TX, Indiana, Virginia, Washington, D.C., Iowa, Wisconsin, Minnesota, and Pennsylvania. Populations of grey squirrels in which the black subgroup is predominant can be found in these six areas as well as in smaller enclaves in Missouri, New Jersey, Delaware, southern New York, Illinois and Connecticut. Outside areas of North America where black squirrels occur naturally in abundance, there are several notable introduced populations of black squirrels:
In the United States, the city of Kent, Ohio developed a significant black squirrel population after ten were legally imported from Canada in February 1961 by Larry Woodell, the head groundskeeper at Kent State University. They have driven out native squirrels in many areas, though they peacefully coexist with most other rodent wildlife.
Black squirrels are well established in the Quad Cities area along the Iowa-Illinois boundary. According to one story, recounted in the book The Palmers, they were first introduced on the Rock Island Arsenal Island. Some of them then escaped by jumping across ice flows on the Mississippi River when it was frozen, and thus populated other areas in Rock Island. In Council Bluffs, Iowa, there is a sizeable population of black fox squirrels, where the animal is the town mascot. Black squirrels are also found nearby in Iowa City. Black squirrels occur in increasing abundance in the cities of Omaha and Lincoln Nebraska, and in the surrounding areas where eastern gray squirrels are not found.  
Black squirrels are abundant in Battle Creek, Michigan, and, according to legend, were first introduced there by Will Keith Kellogg, founder of the Kellogg Company, in an effort to destroy the local population of red squirrels. The story continues that this same population of squirrels was further introduced to the campus of Michigan State University by John Harvey Kellogg for the same purpose. This story was corrected by Wilbur C. "Joe" Johnson, the late chief wildlife biologist at M.S.U.'s Kellogg Biological Station near Battle Creek which includes W.K. Kellogg's former 32-acre estate at Gull Lake. Johnson, who worked at K.B.S. for 48 years, credited Dr. John Harvey Kellogg for introducing the black squirrel to the Kellogg estate during the 1930's. Johnson said he himself trapped 20 black squirrels at Gull Lake during the early 1960's at the specific request of former MSU president John A. Hannah and released them on the East Lansing campus.
The black squirrel has become the predominant squirrel species In Van Wert, Ohio—descendants of several examples reputedly trapped in Michigan during the 1970's by two local residents who wanted to prove their existence to disbelieving friends.
Black squirrels were introduced to Stanley Park in Westfield, Massachusetts, in 1948, having been brought from Michigan as a gift to a local business man. The squirrels are thriving in the park as of 2015. They have also been recently (2016) spotted in Washington State on the northern Olympic Peninsula.
Marysville, Kansas has a notable population of black squirrels which legend claims arrived there by escaping from a travelling circus. The city of Hobbs, New Mexico attempted to introduce black squirrels from Marysville in 1973. However, the new population of black squirrels did not survive, likely having been killed by local fox squirrels shortly after their introduction.
Eighteen Canadian black squirrels were released at the National Zoo in Washington, D.C., near the beginning of the 20th century during President Theodore Roosevelt's administration. Since their introduction, the population of black squirrels in and near Washington has slowly but steadily increased, and black squirrels now account for up to half of the squirrel population in certain locations, such as the grounds of the Washington National Cathedral.
Vancouver has a growing population of black squirrels after they were introduced to the Stanley Park Peninsula before 1914. The squirrels have thrived and spread throughout the Vancouver area and into Whatcom County, Washington.
Black squirrels can also be found in the United Kingdom, where grey squirrels were first introduced from North America at the end of the 19th century. The origin of the UK's black individuals has been a topic of dispute, with initial research indicating that black-colored individuals are descendants of zoo escapees. Regardless of their origins, the black squirrel population in the UK continues to grow, and around the towns of Letchworth, Stevenage and Hitchin, as well as nearby villages such as Shillington and Meppershall in England, black squirrels are now as abundant as grey individuals. Black squirrels have been present and studied in Cambridgeshire since the 1990's; in the village of Girton three quarters of the squirrel population is black. There is some concern regarding black squirrels living in Britain since they can carry Squirrel parapoxvirus which is deadly to the indigenous red variety of the species and can damage local trees. 
There is a large population of black squirrels in the Stuyvesant Town–Peter Cooper Village development in Manhattan, New York City. Some residents of this large residential development have nicknamed the black squirrel a "sqrat".
Mascot and symbol
Though black squirrels are common or predominant in many areas of North America, their overall rarity (perhaps as few as 1 in 10,000) has caused many towns, cities, colleges, and universities to take special pride in their populations of black squirrels. Several cities and towns in the United States and one in Canada make efforts to publicly promote their local populations of black squirrels.
- Detroit, Michigan and Lansing, Michigan
- Middletown, Connecticut
- Marysville, Kansas
- Westfield, Massachusetts
- Council Bluffs, Iowa
- London, Ontario
- Toronto, Ontario
- Kent, Ohio
- Glendale, Ohio
- Charleston, West Virginia
Several colleges and universities in the United States promote the black squirrel as an official or unofficial mascot:
- Haverford College where the black squirrel is the official mascot of varsity athletics
- Kent State University which each year holds a Black Squirrel Festival (located in the Risman Plaza during the second week of September) to honor the university's growing black squirrel population. It features live music, vendors and an overall tribute to the black squirrels seen throughout the campus. Beyond the festival, other businesses and organizations in Kent are named for the black squirrel, including Black Squirrel Brewing Company, Black Squirrel Radio and Black Squirrel Books, an imprint of the Kent State University Press.
- Albion College where the black squirrel has become a significant symbol on campus
- Sarah Lawrence College where the campus coffee shop is named for the black squirrel. The black squirrel is also used as an unofficial mascot, with the bookstore selling plush squirrels.
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