The Squirrel

Three species of tree squirrels are common the the Northeast Illinois region. The Eastern Gray Squirrel, the Red Squirrel and the Fox Squirrel. All are small mammals characterized by a long, bushy tail, prominent ears, and long hind feet. None of the tree squirrels hibernate, but they do have periods of reduced activity during severe cold weather.

All of the tree squirrel species are found in wooded areas. Fox squirrels inhabit the forest edge or wooded areas with little understory. Gray squirrels inhabit mature forests with understory. Fox and gray squirrels are common in towns and cities, especially in parks and residential neighborhoods. Red squirrels prefer dense stands of pine trees but also inhabit mixed forests or oak, maple, hickory hardwood forests with dense understory.

Fox squirrels are common throughout Illinois, even in urban areas. Loss of mature, wooded habitat has decreased the population of gray squirrel in Illinois, although they remain common throughout the state and are locally abundant in urban areas. Red squirrels are found only in the northeastern part of the state, particularly along the Kankakee and Iroquois Rivers.

Each squirrel species has two breeding seasons, one in winter and the other in late spring or early summer. Female fox and gray squirrels that are at least two years old have two litters per year, younger females have only one litter per year. Average litter size is two to four, with young weaned around eight weeks of age.

Fox and gray squirrels have similar food requirements. In fall and winter, acorns, hickory nuts, osage orange fruit and walnuts are important food sources. In winter and early spring, squirrels may eat tree buds or bark if other food is scarce. Both fox and gray squirrels cache (store) food for later use by burying it. Fruits, berries, and corn are important summer food sources. Squirrels will also eat insects and other animal matter. Flying squirrels will eat bird eggs or nestlings, and scavenge for other animal matter when it is available. Red squirrels depend heavily on coniferous trees for buds and seeds from cones, but otherwise eat a diet similar to that of the other tree squirrels. They cache their food in small holes or cracks in the bark of trees.

Fox, gray, and red squirrels are diurnal meaning that they are active during the day. All tree squirrels are active year round, although they will take shelter in their nests during extreme cold weather. Fox and red squirrels spend more time on the ground than gray squirrels. All tree squirrels are solitary; however, since they are not territorial many may be seen in close proximity to each other, particularly if there is a good supply of food. The young often stay near the female until the next litter is born. Nests in tree cavities are preferred, but when cavities are not available squirrels will build nests of leaves in trees.

Like most rodents, tree squirrels have a relatively short lifespan. Most live only a year or two. Hawks, owls, foxes and coyotes all depend on squirrels as a food source.

Squirrel Related Diseases

Tree squirrels in Illinois are not considered to be a public health concern. They can be carriers of various parasites, but none have serious public health implications. It is common to see squirrels with patches of fur missing. Hair loss in squirrels can be caused by mange or fungal disease. Mange is a disease caused by microscopic mites that burrow under the skin. The squirrel mange mite (Notoedres sp.) has been reported in both fox and gray squirrels. There have been no reports of this type of mange being transmitted to humans or domestic pets. Loss of hair, and dark, thickened skin are symptoms of mange in squirrels. Mange can be spread by direct contact between squirrels. Adult squirrels in good condition typically survive mild infestations, but severe infestations can be fatal. Additionally, infected squirrels with a lot of hair loss may die of exposure during the winter. Another possible cause of hair loss in squirrels is fungal disease. A variety of fungal diseases affect squirrels. The fur of infected squirrels will break off at the skin leaving patches of skin that appear to be bare. Otherwise healthy squirrels will recover from fungal infections.

Squirrel exclusion

Squirrels are excellent climbers and jumpers. They are well known as unwelcome guests at birdfeeders. Besides consuming seed, they may damage bird and wildlife feeders by chewing on them. They may also occasionally damage lawns when caching food for the winter. They will also sometimes damage garden plants, particularly corn. While inconvenient, these behaviors can usually be handled by modifying the habitat or excluding the squirrels. In urban areas, squirrels may cause substantial property damage when they chew through siding or enlarge openings to gain access to attics. Once inside a building they may do further damage if they chew on insulation or electric wiring. Squirrels may also cause power outages when they short out transformers. It will likely be necessary to use several techniques to control property damage by squirrels. Exclusion is typically the most effective method when dealing with squirrels.

For more information, including recommendations on removal and exclusion of Wildlife common to the Northern Illinois region, click on any of the links below: