Three species of Illinois ground squirrels are described here. All ground squirrels are characterized by a tail covered with hair, nesting in underground burrows, and internal cheek pouches. Most ground squirrels hibernate and all four species are active during daylight hours. Ground squirrels avoid burrowing in areas subject to flooding.
The eastern chipmunk is the smallest Illinois ground squirrel at two to five ounces in weight and eight to 12 inches in total length. Eastern chipmunks have conspicuous light and dark stripes on the back, sides, and cheeks. The fur on the upper parts is reddish-brown with rust color on rump and flanks. The belly and sides are buff to white. The ears are rounded and erect. The tail is covered with fur but is not bushy and is somewhat flattened. Chipmunks have internal cheek pouches that are used to transport food or excavated soil. The chipmunk does not hibernate. Because they have limited digging ability, they often "burrow" under rocks, logs, or buildings.
Thirteen-lined ground squirrel
The thirteen-lined ground squirrel is slender with large eyes and small ears. They have yellowish fur and 13 prominent alternating light and dark stripes on the back and sides. The light stripes are yellow to white, and the dark ones are black to reddish-brown with lighter spots. The thirteen-lined ground squirrel hibernates in winter. In the fall before hibernation, thirteen-lined ground squirrels weigh eight to nine ounces and are much larger than a chipmunk. However, by spring when the squirrels come out of hibernation they weigh only four to five ounces.
Franklin's ground squirrel
The Franklin's ground squirrel is a little larger than the thirteen-lined ground squirrel, weighing one to one and a half pounds in the fall before hibernation. Franklin's ground squirrels resemble gray squirrels but have a shorter, less bushy tail and smaller ears. They have brownish-gray fur speckled with black and the underparts vary from yellowish-white to gray or buff. The Franklin's ground squirrel is listed as a state threatened species in Illinois.
The Franklin's and thirteen-lined ground squirrels are found in grasslands or prairies while the eastern chipmunk lives in wooded areas. Eastern chipmunks prefer woodland borders rather than deep forests, particularly sloped areas with woody underbrush. Thirteen-lined ground squirrels live in short grasslands or in weedy areas with short vegetation. They are often found in golf courses, cemeteries, parks, or roadsides. Franklin's ground squirrels are found in slightly taller grass, but prefer the grass to be short enough to allow them to stand on their hind legs and see over the grass.
Distribution and Abundance
Eastern chipmunks occur throughout Illinois where there is suitable habitat, although they appear to be absent in the southeastern counties. Thirteen-lined and Franklin's ground squirrels occur in the northern two-thirds of Illinois. The southern limit of these ground squirrels in Illinois seems to correspond with the Shelbyville glacial moraine. Eastern chipmunks and thirteen-lined ground squirrels are abundant in many areas of Illinois but Franklin's ground squirrels are uncommon and are listed as a threatened species within the state.
Like tree squirrels, the eastern chipmunk has two breeding seasons, one in spring and the other in late summer. Chipmunk gestation is 31 days with five to six young per litter. Chipmunks are weaned at six weeks of age. Thirteen-lined and Franklin's ground squirrels have only one litter per year, usually in late May. Gestation is 27 to 28 days with six to seven young per litter. The young are weaned in about four weeks.
Eastern chipmunks feed primarily on nuts, seeds, fruits, fungi, flowers and buds. They cache (store) their food in their burrows. During summer, chipmunks also eat invertebrates such as beetles, grasshoppers, and spiders. Thirteen-lined ground squirrels feed extensively on grasses, weeds, seeds, cultivated plants, and insects. Franklin's ground squirrels are omnivorous. They eat carrion, insects, bird eggs, small birds, and plant material.
Ground squirrels are diurnal meaning that they are active during the day. All squirrels are solitary; however, since they are not territorial many may be seen in close proximity particularly if there is a good supply of food at that location.
There are currently no repellents registered for use against ground squirrels in Illinois.