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Chipmunk (Least / Colorado)
Colorado alone has five chipmunk species, so a chipmunk in the Mountain West is not one animal. The least chipmunk (Neotamias minimus) is the smallest chipmunk in North America and the most widespread one in Colorado, running from sagebrush basins up through timberline and above. The Colorado chipmunk (Neotamias quadrivittatus) is the larger, orange-shouldered animal of the southern Rockies and the Colorado Plateau, and it sticks to rock and to pinyon-juniper and ponderosa country. For a homeowner the burrow, the damage, and the prevention advice are the same for either one, and the places the two genuinely differ are worth knowing instead of pretending they are one animal. Two things are worth knowing before anything else. Neither of them is a golden-mantled ground squirrel, and the fastest way to prove it is the face: a chipmunk has stripes on its face, and a golden-mantled ground squirrel has none. And neither of them hibernates the way a marmot does. The least chipmunk does not lay down meaningful fat in the fall at all. It caches food, then spends winter cycling in and out of torpor, waking to eat from the cache, and it can turn up above ground on a mild January day.

Seasonal Timeline

Both species are active by day from spring through fall, with the heaviest caching push in autumn as animals build the food stores that carry them through winter. Timing is set by elevation and snow rather than by the calendar, which matters a great deal here, because a single Colorado mountain can hold sagebrush-basin chipmunks and alpine chipmunks on completely different schedules. Breeding begins within about a week of emergence, whenever snowmelt reaches that elevation. Through winter the animals cycle in and out of torpor rather than sleeping straight through, and some come above ground when the weather is mild.

Peak, Every regionApr–Jun
Peak, Every regionSep–Oct
JanFebMarAprMayJunJulAugSepOctNovDec

Both species are active by day from spring through fall, with the heaviest caching push in autumn as animals build the food stores that…

No source publishes region-by-region seasonality for either species. The timing below comes from published biology instead.

Elevation, not the date, is what sets local timing. A study at 3,018 meters in Colorado found males emerging as snow-free ground appeared, and at the height of snowmelt in mid-May, 80 percent of 30 males were in breeding condition and were believed to be the only males that would breed that year. Of 18 females taken at that same peak-snowmelt moment, 4 were already pregnant, 9 were in estrus, and 5 were nonbreeders. Females enter estrus within about a week of emergence, meaning their reproductive organs prepare for breeding while the animal is still sealed in its winter den. In Wyoming, mating ran from 8 April to mid-May with the latest birth on 16 June. Across Colorado as a whole, most breeding is placed from late March to early July, and that wide window is the elevation spread, not sloppy data.

The same logic runs horizontally across the range. Aboveground activity was recorded from 30 April to 17 October in northern Alberta, from mid-April to November in Manitoba, and from mid-March to early November in Wisconsin. Latitude and snow cover set the onset and end of torpor bouts. In the Mountain West that gradient runs vertically instead, up a single mountainside.

Where They're Found

Both animals are outdoor, ground-level residents. No source documents either species nesting inside a structure, in an attic, or in a wall void, which is the single most useful thing a homeowner can know before calling anyone.

Inside the Mountain West, the two species divide the map. Colorado Parks and Wildlife states that the least chipmunk lives over most of the central and western parts of the state and is the most widespread chipmunk in Colorado, while the Colorado chipmunk lives in southern Colorado and northward along the foothills of the Eastern Slope nearly to Wyoming. Colorado holds five chipmunk species in all: Colorado, Hopi, Uinta, cliff, and least. The state's own profile is blunt that chipmunks are not easy to tell apart from each other in the field, which is exactly why the two most likely species are treated together rather than split with a precision the state itself does not claim.

Elevation is where the two really separate. Least chipmunks have been recorded above 3,500 meters, roughly 11,500 feet, and Rocky Mountain National Park runs them from the lowest park elevations to timberline and above. The American Society of Mammalogists species account for Colorado chipmunk states that its elevational range on the eastern slope of the Rockies is more restricted than the least chipmunk's. Where the two occur together, the Colorado chipmunk is the one recognized by its larger size and its affinity for rocky sites rather than wooded ones.

On the ground, look at the cover, not the lawn. Least chipmunk habitat across a huge range has one common element: it is relatively open near ground level. Studies found the species selecting habitat where cover in the first 15 centimeters above the surface was sparse, which allows fast escape from aerial predators. Documented Mountain West specifics include streamside, rock cliff, rock slide, and alpine habitats within the sagebrush, spruce-fir, and pine belts of the Uinta Mountains in Utah and Wyoming; aspen groves and rocky outcrops; and in Nevada's Ruby Mountains a distribution limited only by the absence of sagebrush. Notably, least chipmunks were rarely taken in fir and spruce forest in Colorado. Colorado chipmunk is the coniferous woodland and rock animal of the pair, and at lower elevations in pinyon-juniper woodland it is tied specifically to rock.

The burrow itself is small and easy to miss. In Colorado, entrances dug by least chipmunks averaged 3.7 centimeters across, about an inch and a half, with a standard deviation of 1.1 centimeters across 29 measured entrances, and burrows averaged just 1.3 entrances apiece. Interior chambers run about 15 centimeters across. Around a home the same conditions come from rock walls, retaining walls, boulder and talus edges, woodpiles, brush piles, log heaps, and unbroken shrub or ground-cover plantings running from wild ground straight up to the foundation.

Beyond the Mountain West. Both species range well outside the Mountain West. Least chipmunk runs from west-central Yukon south along the east base of the Rockies and east to Hudson Bay, James Bay, southeastern Ontario, and Michigan's Upper Peninsula, taking in eastern Montana, South Dakota, Minnesota, southern Idaho, eastern Washington, east-central California, southern Nevada, central Utah, northeastern Arizona, and northern New Mexico, with disjunct populations farther south. Colorado chipmunk runs the mountains of Colorado and eastern Utah south to northeastern Arizona and southern New Mexico. The eastern chipmunk, covered on its own page here, is a different genus entirely and does not occur in the Mountain West.

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