Are there any chipmunk experts here on the SDMB? How do you tell the difference between the Least Chipmunk (Neotamias minimus) and the Colorado Chipmunk (Neotamias quadrivittatus) in the field? Their ranges overlap here in northern New Mexico. I know the Least Chipmunk is slightly smaller than the Colorado Chipmunk but what if it is a juvenile Colorado Chipmunk? A couple of people have told me that one clue is the way they hold their tails when they run. Is this true? I suspect that some people that post chipmunk photographs on the Internet are themselves confused and mislabel some photographs.
I found this weird dump of text including versioning changes I think, as part of an unrelated web site. I don’t know if it’s worth looking at but it did include a phone number which turns out to be for the Rocky Mt. National Park, (970) 586-1206. So maybe email them and see if they can point you to a good resource.
Based on this little bit of info it appears identification will be difficult:
Colorado chipmunk wiki - “This western American dweller is the largest of the three species of chipmunks found in the Colorado Front Range (which also include the Least Chipmunk and the Uinta Chipmunk). On average it weighs about 62 grams (2.2 oz).”
Least chipmunk wiki - " It is the smallest species of chipmunk, measuring about 15.7–25 cm (6.2–9.8 in) in total length with a weight of 25–66 g (0.88–2.33 oz)
So the smallest species of chipmunk, the Least, may outweigh the largest of the local species, the Colorado.
And the Least may also be indistinguishable from the Yellow Pine chipmunk - “In some areas, where range overlap with the yellow-pine chipmunk occurs, it may be difficult or impossible to distinguish the two species in the field; laboratory examination of skeletal structures may be required.”