Why are there so many black squirrels in Detroit, and why are they so prone to nesting in homes?
This morning, upon dropping our son off at kindergarten in Detroit's Marygrove neighborhood, my husband and I witnessed EIGHT black squirrels in a single front yard! This observation led us down a research rabbit hole as we asked the question; “why are there so many black squirrels in Detroit and why are they so prone to nesting in homes?” We concluded that there are several main causes including climate pressures, the French fur trade of the 17th and 18th centuries, and urban development.
The black squirrels that are so prevalent in the Detroit area are the result of interbreeding between northern Grey squirrels and red fox squirrels that results in a missing pigment gene on the DNA of the offspring resulting in the black pigment. This pigment is thought to improve heat retention in cold climates because of absorption of UV energy from the sun. Scientists therefore believe these types of squirrels would have an advantage surviving the extreme temperature shifts of the Great Lakes region.
However, when one looks at the map of black squirrel population in the US you'll find these animals aren't common in other northern regions in the US nor are they as common within Michigan outside of the Metro Detroit region.
Looking at this map I noted that it seems to nearly follow French Fur trade routes of the 17th and 18th centuries. Detroit was a primary stop on these trade routes and received its name from these traders. Given this information, I researched the trade of squirrel furs during this era and found that gray squirrel pelts were the most valuable from this area, and traded at much higher rates than black squirrels, with brown squirrel pelts trading at only a slightly lower rate than gray squirrel pelts. Josh did a little digging and learned that squirrels were rarely trapped like many animals used in the fur trade, but were shot using a single-shot musket. This would mean that these lower value animals wouldn’t be killed at nearly the rate of gray squirrels because they weren’t worth the opportunity cost of shooting at them. It would follow then that gray and brown squirrels were being removed from the population by 17th and 18th century fur traders at a higher rate than their black cousins. This would eventually result in increased interbreeding with these black squirrel variants. This would result in higher black squirrel populations along this entire fur trading zone which is what we see in modern populations of black squirrel populations in this region
With 8 years of experience removing squirrels from attics, chimneys, garages, and other human structures Josh has always noted that there are more black squirrels in the city than the suburbs. I also had anecdotally noticed there are just more black squirrels in Detroit. A few years back, while chaperoning a field trip with a group of Detroit high school students to the northern part of Michigan, I noted how many of them were surprised with all the gray and brown squirrels that populated the old growth forest we were learning about. I remember one girl saying she didn’t realize squirrels came in different colors. The French Fur Trade route couldn’t explain these discrepancies, so I did a little more digging about black squirrel behavior. It turns out that urban areas help black squirrels to be prolific. Because the black fur is poor camouflage for more wooded environments, black squirrels stick out visually and are targeted more by predators. This leads to much lower populations of these rare genetically mutated black squirrels in more rural portions of these old fur trade routes. Additionally, given the comparative prevalence of drivers in urban regions, the high visibility of the black squirrel would allow drivers to avoid collisions with these animals more frequently than their gray and brown counterparts.
All of these pressures contribute to why the black squirrel is so prevalent in Detroit, but why do they want to live in your attic? Black squirrels, like their gray cousins, like to nest between 20 and 30 ft from the ground to avoid predators. Unfortunately, there aren’t many of these big old trees in the urban areas where Black Squirrels are most concentrated, so they end up in the tallest thing in their habitat, your home’s attic, soffits, gutters, and roof. They treat these structures as they would a tree and chew a hole in to find a warm place as shelter. If this happens to your home, please call Morrison and Sons Pest control for affordable, quick, and humane removal of these rare special animals so we can take them out of your attic and place them in a place with tall trees where they won’t be a nuisance to anyone. Afterwards, you can count on us to seal up the damage and prevent future squirrels from taking up residence.
If you want to learn more about black squirrels in Detroit, here are my sources:
https://meanderingmichiganhistory.weebly.com/fur-trading-on-the-detroit-river.html
https://www.mentalfloss.com/article/596445/why-some-squirrels-are-black
https://www.michigan.gov/dnr/managing-resources/wildlife/wildlife-disease/wdm/squirrel-pox
https://www.british-history.ac.uk/london-record-soc/vol38/pp133-155
https://www.british-history.ac.uk/london-record-soc/vol38/pp215-229
https://www.nps.gov/parkhistory/online_books/voya/futr/ch3b.htm
https://www.militaryheritage.com/musket28.htm
