by Whit Gibbons

February 26, 2012

Several people have asked recently why they have seen so many squirrels dead on the road. Could the answer be as simple as that gray squirrels have engaged possums in a contest to be proclaimed king of the roadkill? Possums ordinarily win the I-got-hit-by-a-big-truck awards, but squirrels seem to be vying for the record in some areas. Do some of today's smooth-running cars sound like sunflower seeds being sprinkled into a bird feeder?

A more likely explanation is a biological trait of squirrels that resembles lemmings, which have been reported to make mass migrations after increasing to high densities in a region. Records from the 1800s report thousands of squirrels traveling overland in the same direction, and recent records exist of smaller mass migrations. Some trips ended only when they reached a river too wide to swim. The cause of the phenomenon remains unknown. These days, busy highways are effective stopping points in addition to rivers, resulting in flattened squirrels rather than drowned ones.

Gray squirrels live in practically every city in the eastern United States where hardwoods are found; they thrive around people. Parks where pigeons and squirrels live off nuts and popcorn provided by tourists are ideal habitats. The highest population density of squirrels ever reported was not from a forest but from Lafayette Square in Washington, D.C.

Less obvious tree-dwelling squirrels in North America include fox squirrels, red squirrels, and flying squirrels, and the ecology of each is different. Gray squirrels in the South usually begin mating in January. Females have a gestation period of about six weeks, normally producing a litter averaging two to three young in February. Babies are born hairless, with their eyes closed. They leave the nest about two months later after being weaned. So, by early summer, a whole new generation of birdseed eaters has been added to local squirrel populations. Meanwhile, supplementing food supplies for suburban squirrel populations probably results in mothers producing larger litters and also having a second litter during late summer or fall, thus further increasing the squirrel population size.

Gray squirrels are not always gray. They also come in black and in white. I saw a white one last week in a forested area near Charleston, S.C. And I lived around a population of mostly black individuals on Michigan State University's W. K. Kellogg Biological Station, formerly the estate of the Corn Flakes magnate. Kellogg reportedly was partial to a black phase of gray squirrel found in small numbers in the area and had the gray individuals eliminated. The black phase is now the prevalent color pattern in the region as confirmed by the fact that most of the road-killed squirrels in the area are solid black. White squirrels, usually a result of albinism, also may become more abundant in a neighborhood than the normal gray phase because people make special efforts to protect them as an oddity.

Gray squirrels, whose natural geographic range is North America, now thrive in England, where many people view them as pests. Having no natural predators in England, a few American gray squirrels brought to London successfully colonized. Their sins include eating bark off native trees, destroying shrubbery, and generally being a bloody nuisance. The British seem to have no end of colonists being pests.

Gray squirrels are indicted by some as a U.S. pest, too, especially by suburban residents who like to feed birds. As all who put out bird seed know, when gray squirrels are around they, rather than birds, become the primary customers. Logically, since birds can fly and gray squirrels cannot, a seemingly simple solution would be to suspend the bird feeder from a tree limb or mount it on an unclimbable pole. Logically, yes. Realistically, no. Squirrels can compete with monkeys in agility and are superb competitors with birds when going after sunflower seeds. My approach for dealing with squirrels at bird feeders is a simple one--learn to enjoy the squirrels. Maybe if they are well fed enough, they won't be crossing the road to find a better meal.

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