Gray squirrels are not always gray
By Robert A. Hedeen
By Robert A. Hedeen
When was the last time you saw a black squirrel in the Rock River Valley? The other day, while looking out the window at the squirrel feeder I have in my wooded backyard in Loves Park, I saw a black squirrel avidly shucking an ear of corn I had provided. I immediately recognized it as a mutant, melanistic, gray squirrel; the first one I had seen in the some 13 years I have lived in Cook and Winnebago counties
In former years, the melanistic variety of the gray squirrel (Sciurus carolinensis) was much more abundant in this area than it is today. In 1857, a biologist by the name of R. Kennicott reported that of some 50 squirrels shot near the Rock River, all were black. At the present time, there are a few black squirrels to be found locally, but nowhere near that high a percentage of the population. In fact, in 1978 C. M. Nixon and two of his colleagues at the Illinois Natural History Survey reviewed the known localities where melanistic grays were found, and Winnebago County was not included. They reported populations of melanistics from Jo Daviess, Carroll, Rock Island, Adams, and Cook counties, with the greatest number being found along Lake Michigan from Evanston to Zion. It is generally believed that melanistic gray squirrels survive only where they are protected from hunting, as in cities and forest and park preserves.
In nature, if a mutation from the norm is to survive, it must be non-detrimental to the animal in which it occurred. The normal coat pattern of the gray squirrel evolved over countless generations while natural selection determined which body coloration gave the most protection to the animal from its enemies. I would hazard a guess that the genetic mutation from gray to black is more or less a neutral change, being neither advantageous nor disadvantageous to the squirrel in its constant struggle for survival. Being neutral, the process of natural selection would have little if any effect on a melanistic squirrels potential for survival.
As most mutations are termed recessive by geneticists, two recessive genes are required to produce the trait. For example, if each of two gray squirrels carry a single recessive gene for melanism, one in four of their offspring would predictably be black. Only one dominant gene is required for the expression of the trait it controls.
In biological islands, where mating and the interchange of genes is restricted to a few isolated individuals, mutant individuals can dominate the population. I have seen such a situation in a park in downtown Mobile, Ala. where melanistic squirrels form almost 100 percent of the population. The park is a genetic island for black squirrels, and they interbreed with no inflow of dominant gray genes from the outside. A similar situation can be found at the Rock Island Arsenal located on an island in the Mississippi River at Rock Island.
When was the last time you saw a pure white or albino squirrel in the Rock River Valley, or anywhere else? Not recently, I would suspect. Albinism is another recessive mutation that occurs in most living things, both plants and animals including humans. In true albinism there is a lack of any pigment in any part of the body of the organism. The eyes of an albino animal appear red; not from a red pigment but from the blood in the vessels showing through the transparent cornea.
Albino squirrels occur in all parts of Illinois, but it is a safe bet they usually do not live to a ripe old age. Where melanism is a neutral mutation, albinism is certainly a disadvantageous change. An all-white squirrel is easily spotted by a hawk, owl, or other predator looking for its next meal. However, in a few locations, populations of white squirrels have managed to survive. Albino gray squirrels have been established for many years in Olney in Richland County. There are various stories of how this colony of albinos originated and how it has survived. One of the most colorful of these accounts is that around 1902, a local trapper snared a pair of living white squirrels and placed them on exhibition in an Olney saloon. An early animal rights activist supposedly rescued the pair and released them within the city. The pair was adopted by the local population, and protective measures were instigated to ensure their survival.
By 1950, the original pair had successfully given rise to an estimated 650 whities, and by 1971 (the latest Olney squirrel census available), that number had increased to about 1,000. It is suggested that if anyone has an overpowering urge to see an albino squirrel, he visit the city of Olney; finding one in Winnebago County would be highly improbable, though not impossible.
It has been estimated that since Illinois was first settled by Europeans, 75 percent of the forests have disappeared, and in some of the remaining forests the understory, which is vital habitat for squirrels, has been removed. This has resulted in a great reduction in gray squirrels in all parts of Illinois, probably more than 75 percent.
We can be thankful for forest preserves and park districts throughout the state which provide a safe haven for squirrels and other forms of wildlife from the never-ending advancement of civilization.
Dr. Robert Hedeen is a former resident of eastern Maryland, with degrees in zoology and botany. He is a former professor of biological science. He has had 30 scientific papers published, has written numerous magazine articles, and is the author of two books on marine biology of Maryland.