Colorado chipmunks are solitary and territorial, and adults avoid each other except during the breeding season. Males emerge from their burrows in the spring ready to mate. Females emerge a week or two later, and are receptive for only a few days. Gestation lasts about a month, and the young first appear aboveground when they are about 25 days old and three-fourths adult size. Sometimes Colorado chipmunks breed again in the summer and have a second litter. They are a great deal like least chipmunks in their activity cycles, reproduction, foraging behavior, and vocalizations, but curiously enough, when a Colorado chipmunk vocalizes it sways its tail from side to side, and when a least chipmunk vocalizes it flicks its tail up and down.

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account