Can you tell the gender of a chipmunk from a distance?
We have a large number of chipmunks, probably mostly Eastern Chipmunk, Tamias striatus, in our yard in Massachusetts. There are different sizes and a large variation in markings. The behavior appears similar, so the gender isn't obvious.
They all have names, including Long-tail Chip; Short-tail Chip; Chubby Chip; Skinny Chip; Dark-striped Chip; Light-striped Chip; Pointy-head Chip; Speedy Chip; Lazy Chip; Silly Chip; Brave Chip; Shy Chip. They're all Smart Chip, because they're brilliantly adept at getting into bird feeders and tall pots. They can also reach, and eat their way though, plastic bags of food and nuts which are 6 feet up on shelves in the garage.
Without picking them up, is there a way to tell a male from a female?
Update as of April, 2017: Four weeks ago a very pregnant chipmunk popped up out of a hole in the snow. We memorized her markings to the best of our ability. We saw her again a few days later. Since then, we've been feeding her near that hole every day. She dutifully gathers up the seeds and corn and pops back down. Since the babies stay in the nesting burrow for six to eight weeks, she'll probably keep feeding them until then. In the meantime, many other chipmunks are now very active in the yard. There's a wide variety of sizes, shapes and colors, and there are holes everywhere. The only way we know about the female is that we saw her when she was pregnant.
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I live on Cape Cod and have hand fed Tamias Striatus for over a decade. I identify individuals and name them and know their lineage and personal habits, where they live, when they create new burrow entrances, etc. I have kept a fairly detailed log for most of this time.
Males in breeding season (and often well beyond that time) are easy to distinguish from females. Their scrotal sac is enlarged and obvious from behind and below. I’ve had munks who were in breeding condition most of the Summer, although that is not typical.
Usually this condition only lasts perhaps a month or so. Females just prior to giving birth until some time after dispersal will have 3 or 4 rows of teats on their underside which are visible when they are sitting up. Of course when the female is pregnant she is usually pretty chubby.
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This is not a direct answer, but still relevant.
Technically, "chipmunk" is the common name for a limited few specific species of ground squirrels. These usually have the stripes that run along their sides converge all the way to the nose. There are many more ground squirrels that are not really chipmunks. However, the name "chipmunk" is sometimes applied to any ground squirrel that has stripes on its sides.
The point of all this that if you are trying to search for more information on these animals, widening to "ground squirrel" may lead to better results. It may also help get more scientific write-ups, as apposed to those from people that refer to anything small and furry that scurries around as a "chipmunk".
Usually I find the best way to get good information on particular animals is to use the common names in searches just to get the scientific names. Then use the scientific names to get the real information.
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As to the OP's question:
The answer is Most Probably Not.
From http://www.ct.gov/deep/cwp/view.asp?a=2723&q=345000, a State of Connecticut publication on the Eastern Chipmunk:
There is no difference in appearance between males and females.
From How to tell if the Chipmunk is male or female
•Pick your chipmunk up with your hands and place him on his back, with his rear closest to you. Your chipmunk will probably wiggle and protest, therefore, it may take a few times to successfully keep the rodent on its back.
•Locate the genitals and anus. These features can be found towards the end of the chipmunk and will appear as two distinct bumps.
•Look at the genital area, which is located above the anus. In the genital area, males will have two bumps that are about one centimeter apart from each other. In females, the bumps are touching each other.
This is a pet site. The site did not mention any characteristics as a clue to the gender; it went straight to this procedure. This is not definitive, but if you could tell just by looking at the whole chipmunk, they would most likely have give you some clues before describing this procedure.
It is possible that by close observation of behavior in the spring, you could tell which was male. From Mating Habits of Chipmunks
In April, mature male chipmunks are ready to mate two weeks before females and sometimes compete with each other for females
Addressing Ben Crowell's comment (you may be seeing two species):
From Wikipedia, Eastern Chipmunk
The eastern chipmunk (Tamias (Tamias) striatus) is a chipmunk species found in eastern North America. It is the sole living member of the chipmunk subgenus Tamias, sometimes recognised as a separate genus.
From Wikipedia, Chipmunk
Chipmunks may be classified either as a single genus, Tamias (Greek: ταμίας), or as three genera: Tamias, which includes the eastern chipmunk; Eutamias, which includes the Siberian chipmunk; and Neotamias, which includes the 23 remaining, mostly western, species
It doesn't flat-out say so, but I interpret this as the Eastern chipmunk lives in eastern NA and the other species live in western NA (23 of them) or Siberia. It's that word "mostly" which means we can't be 100% sure that you don't have more than one species. (But we know Ben has a lot.)
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