Family SCIURIDAE 135 



CITELLUS TRIDECEMLINEATUS (Mitchill) 

 Thirteen-Lined Ground Squirrel Striped Gopher 



Description. — The thirteen-lined ground squirrel, fig. 76, is 

 about the size of a chipmunk. The ears are small, the eyes are 

 large, and the slightly bushy tail is shorter than the body. The 

 back has approximately 13 longitudinal stripes alternately dark 

 brown and buff. Each of the brown stripes contains a series of 

 buff spots. The sides of the body are yellowish or buff, and the 

 belly is the same color as the light stripes on the back. 



Length measurements: head and body 5>)4 _ 7-)4 inches (145- 

 2C0 mm.); tail 31/6-4)4 inches (80-110 mm.); over-all 8-M" 

 1 -2 1 4 inches (225-310 mm.); hind foot \\i~\% inches (32-41 

 mm.). Weight: about 4 ounces in early summer; nearly 8 

 ounces in fall prior to hibernation. 



The skull, fig. 13a, is 36-43 mm. (about \\/z inches) long and 

 delicate in appearance. In Illinois, only this squirrel, the gray 

 squirrel, woodchuck, Franklin's ground squirrel, and the south- 

 ern flying squirrel have five cheek teeth on each side of the upper 

 jaw. The skull differs from that of the gray squirrel and the 

 woodchuck by its decidedly smaller size ; from that of Franklin's 

 ground squirrel by its smaller size and by its shorter nasal bones 

 (less than 17 mm. long) ; from that of the southern flying squir- 

 rel by the absence of deep notches in the interorbital region, 

 fig. 73a, by incisors that have yellow rather than reddish front 

 faces, and bv smaller auditory bullae. Dental formula: I 1/1, 

 C 0, Pm 21, M 3/3. 



Life History. — In the northern half of Illinois, the thirteen- 

 lined ground squirrel is seen through casual observations per- 

 haps more often than any other wild mammal during summer 

 days. Members of this species attract attention as they dash 

 across highways or as they stand stiffly erect near the entrances 

 of their burrows on golf courses, in pastures, in cemeteries, and 

 on grassy roadsides. The shortness of the grass in areas where 

 they prefer to live makes them conspicuous, fig. 2. Loud noises 

 or sudden movements may cause them to run for their burrows. 

 A ground squirrel may give its shrill, quavering whistle of alarm 

 before disappearing underground. 



So great is its curiosity that a thirteen-liner cannot long re- 

 main hidden. Soon it will be peering out of the mouth of its 

 burrow and before much Longer it will be back at its usual 



