As part of our initiative called Curious Cornhuskers, an anonymous reader asked The Daily Nebraskan, “Why are there black squirrels?”
Due to a genetic mutation, the black coats result from more pigment — a protein that absorbs light and presents a darker appearance — in the fur, according to Chad Brassil, an associate professor in the School of Biological Sciences. Over time, the mutation has been passed down through offspring in the fox squirrel population.
Both the red, rufous-colored squirrels and the black-colored squirrels found on the University of Nebraska-Lincoln campus are fox squirrels, just with genetic variations that lead to different colors of fur, he said.
Mutations occur through an error of replication during reproduction, Brassil said, and are usually not advantageous to a species. Whereas albinism results in a white color due to a complete lack of pigment, melanism is the increased production of melanin, a group of a dark pigment that results in darker skin, hair or fur color.
Natural selection takes over after a mutation occurs and determines whether it will be passed on. Due to an increased level of fitness, the black fur mutation proves beneficial and has become a trait for the fox squirrel species, Brassil said.
“Most mutations are bad, and they cause things to break because the organism is a complicated system,” Brassil said. “Occasionally, instead of being bad, there will be a mutation that doesn’t cause things to break and maybe makes things a little bit better.”
After reproduction, he said the baby squirrel will have two sets of genetics and alleles, different variations of the same gene, that dictate fur color. If a black squirrel mates and reproduces, the offspring’s fur could be black.
Brassil said the squirrels have not yet gone through fixation, where all squirrels may have the allele, but said that may occur over time, or there may be an advantageous purpose that arises that justifies having two colors of fur.
Three main theories exist, he said, as to why the mutation occurred in the past and remains a beneficial mutation: a thermal advantage, a predator avoidance advantage and a human preference that together equated to a higher number of black squirrels.
In the United States, there are two main populations of black squirrels around the country in both the northern area around places like Canada, Colorado and Nebraska and in the southeastern area where forest fires are common, Brassil said.
According to Brassil, while the population in the north thrives by absorbing more sunlight during the winter in colder months allowing them to be more active, the southeastern population utilizes dark patches of the environment in burnt forests to hide from predators, allowing them to camouflage within the shadow.
When mutations are beneficial, Brassil said, species can have a slightly higher fitness resulting in an increased capability of producing more offspring and further increasing the likelihood of offspring inheriting the black coat.
“It’s kind of easy to go to black instead of something more complicated because you really just need this one mutation that produces a lot of dark pigment that’s absorbing the light,” he said.
Brassil said humans have also led to an increase in the black coat by introducing the squirrels to new ecosystems around the country and expressing an interest in the black variant. Black squirrels were introduced to the Smithsonian National Zoological Park in Washington, D.C., and to Michigan State University’s campus in the past where they then repopulated and increased in number.
“There’s this thought that some of the locations that we see [black squirrels] are not just through natural movement,” Brassil said. “It has been sped up by humans transplanting them to these other spots, reducing the dispersal barrier of a mutation to move into an area.”
His own personal theory is once these black squirrels reach a new location, some people may find them cute and novel and may preferentially feed them as opposed to the other, rufous colored squirrels in the area, he said.
“It’s all of those things wrapped together with some uncertainty,” he said. “We may not know, but those are our best guesses. It’s an area of science that has an open question.”
What is NUTS?
Fascination has led UNL students to create their own recognized student organization on campus devoted to squirrels: Nebraskan for the Upgraded Treatment of Squirrels.
Teagan Steinmeyer, a sophomore elementary education major and treasurer of NUTS, said she found out about the club when she was in high school and knew she wanted to join when she came to UNL.
At the monthly meetings held on Wednesdays, NUTS members discuss squirrels, join together for fun activities, get to know one another and try to increase member involvement, Steinmeyer said.
Brassil, who is the faculty advisor of NUTS, said the club is a fun place for UNL students to come together and hang out.
“I think it’s great that a group of students wanted to put together a club with no purpose whatsoever just to do quirky, fun things,” he said. “It’s like a quirky social group that has a great sense of humor at its own expense.”
Steinmeyer said most of the members find squirrels interesting, including the black squirrels which are usually discussed at a few meetings. She said the club is fun for anyone who joins.
“We talk about squirrels but we also try to be part of the community,” she said. “If you’re looking for somewhere to make friends, have a good time and talk about squirrels, then NUTS is a great choice.”
College is stressful, Brassil said, but NUTS is a place for all students to come, have fun and talk about squirrels. The club will not meet in December due to the shortened month but will be back next year with more meetings devoted to squirrels and fun.
“Most people look at a squirrel and they find it fascinating,” Brassil said. “It’s a fairly large mammal that is out in the day time … so we see it regularly — we’re comfortable with them. How could you not love them?”