Did you know?
- Ground squirrels are rodents (gnawing mammals) and are placed in the order Rodentia along with tree squirrels, mice, rats, voles, muskrat, beaver, plains pocket gopher, and southern bog lemming.
- Franklin's ground squirrels spend 90 percent of their lifetime below ground.
- Thirteen-lined ground squirrels have been known to hibernate for 250 days.
- Eastern chipmunks stomp their feet and wave their tails to protect their territories.
Description and Identification
Three species of Illinois ground squirrels are described here. The fourth and largest "ground squirrel," the woodchuck, is covered in a separate section. 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.
Eastern chipmunk (Tamias striatus): 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 upperparts 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 (Spermophilus tridecemlineatus): 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 (Spermophilus franklinii): 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.
Damage Prevention and Control Measures
If ground squirrels are causing problems there are several control strategies available. Note: Franklin's ground squirrels are threatened in Illinois and are protected. If you are having a problem with Franklin's ground squirrels call your local IDNR District Wildlife Biologist for assistance.
- Encourage the growth of tall, herbaceous vegetation to deter thirteen-lined ground squirrels from using the property.
- Reduce seed bearing weedy plants that provide food for ground squirrels.
- Keep soils moist through overhead irrigation during the day.
- Prevent digging in seedling gardens by planting cold-tolerant varieties before ground squirrel emergence in early spring.
- Foundation plantings may encourage chipmunks. Check the foundation regularly for signs of burrowing.
- Exclude ground squirrels from small areas by installing 18-inch high one-quarter to one-half-inch mesh hardware cloth (hail screen) buried six inches below ground.
- Chipmunks should be excluded from buildings wherever possible. Use hardware cloth with ¼ inch (0.6 cm) mesh, caulking, or other appropriate materials to close openings where they could gain entry. To keep ground squirrels from burrowing under foundations, place hardware cloth bent at a 90° angle along the foundation and cover with soil.
There are currently no repellents registered for use against ground squirrels in Illinois.
If other control methods have failed, ground squirrels can be trapped and removed. A permit is not needed. Live-traps baited with seed can be used to capture ground squirrels. If you plan to release the squirrel, it should be released five to ten miles away. You will need permission of the landowner before you release the squirrel. Rat-sized snap traps are efficient if ground squirrels are to be lethally removed. Nuisance wildlife control operators will trap and remove squirrels for a fee.
Public Health Concerns
Ground squirrels in Illinois are not considered to be a public health concern. They can be carriers of plague; however, transmission of plague from squirrels is extremely rare. There are only ten to fifteen cases of plague reported in the United States each year, and most of these cases are from western states. For more information about plague, read the Illinois Department of Public Health Plague Factsheet.
Ground squirrels play an important role in soil aeration. They help condition the soil for plant growth. Their body wastes contribute to the organic structure of the soil. Ground squirrels are also an important part of the food web, being preyed upon by several species of birds, mammals, and snakes.
In Illinois, thirteen-lined ground squirrels and eastern chipmunks are not protected by the Wildlife Code. The Franklin's ground squirrel is protected by the Illinois Endangered Species Act.