Ordinarily, one can’t tell a male from a female eastern chipmunk as they look identical –but there are two times during the year when it is possible, with luck and good eyesight, to tell one from the other. One is right now, in the early spring, when chipmunks first emerge from their underground burrows. Male chipmunks appear first, followed by females one or two weeks later. The first of two breeding seasons is beginning for chipmunks. Upon emerging, the males’ testicles descend, making the males distinguishable from the females. Their scrotal sac is covered with whitish-gray fur; the darker the fur the more mature the chipmunk is.
During their breeding season, males travel outside of their home ranges, often some distance, to locate females and check on their reproductive condition. The females chase and wrestle with the males to see who can keep up with them. When a female comes into estrus (the end of February/ beginning of March) she chooses her mate. The chosen male flicks his tail vertically and screams prior to copulation (another way to distinguish the sexes). After the first mating season, the testicles ascend until the second breeding season in middle to late summer, when the chance to determine the gender of chipmunks once again presents itself.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.