Thirteen-lined ground squirrels are sexually mature at 9 or 10 months of age. They mate within 2 weeks after emerging from hibernation. Both sexes are sexually active for about 2 weeks. After a gestation period of 28 days, 3 to 14 (average 10) blind, naked, toothless young are born. Only 1 litter is produced per female each year. The young weigh about 1/10 ounce at birth. Their stripes begin to appear after about 12 days and their eyes open after 28 to 30 days. Young are weaned after 6 to 12 weeks.
The inconspicuous, 2-inch diameter openings to burrows of 13-lined ground squirrels often are concealed by vegetation and rarely have soil scattered in front.
The main entrance plunges down 6 inches or more before angling off into a complex system of galleries and side entrances. The chamber for rearing young is about 9 inches in diameter, lined with fine dry grass, and is located somewhat deeper than the main burrow system. Natural enemies include most predator species, especially hawks, badgers, weasels, foxes, coyotes, bull snakes, and black snakes.
Thirteen-lined ground squirrels are diurnal, coming above ground when the sun is high and the temperature is above 80°F, and returning to the burrow long before sundown. They rarely venture out of the burrow on damp, dark, or overcast days. They often stand upright, with front paws held close to the chest, surveying their territory. If danger threatens, they run with tail held horizontally to the nearest burrow.
Thirteen-lined ground squirrels begin hibernation in September or early October and emerge between late March and early May in the northern portions of their range. Males usually begin hibernation earlier in fall and emerge earlier in spring than females. When they hibernate, their body temperature generally is within a few degrees of the ambient air temperature.
Thirteen-lined ground squirrels prefer grassy areas that are cut low. They avoid wet areas with heavy clay soils. Home ranges of 13-lined ground squirrel vary between 3 to 12 acres. Thirteen-lined ground squirrels do not defend home ranges but will defend dens. Densities of adults can reach 10 animals per acre, and increase dramatically when young emerge.
Thirteen-lined ground squirrels eat vegetation, the eggs and young of ground-nesting birds, earthworms, lizards, mice, and insects. During summer, insects constitute up to ½ of their diet. Thirteen-lined ground squirrels prefer grasshoppers and beetle and moth larvae. They also consume seeds, green shoots, flower heads, roots, vegetables, fruits, and cereal grains. They rarely drink water, depending on moisture contained in their food. They cache large quantities of seeds and grass. The cached food may be eaten during periods of bad weather or when other food is scarce.