Specimens examined (31).—2 mi. N, 5 mi. W Ludlow, 15; NW 1/4 sec. 15, R. 5 E, T. 22 N, 2; 2 mi. S, 3-1/4 mi. W Ludlow, 2; NW 1/4 sec. 32, R. 1 E, T. 20 N, 1; 9 mi. S, 7 mi. W Reva, 1; 10 mi. S, 5 mi. W Reva, 9; NE 1/4 sec. 8, R. 8 E, T. 16 N, 1.
The least chipmunk is common in the buttes and associated badlands where it most frequently inhabits rocky areas. Visher (1914:88) reported E. minimus from Harding County ("abundant in badlands"), but his paper has been overlooked by most subsequent workers. Visher's mention of a chipmunk from the mouth of the Moreau River in north-central South Dakota, incidentally, would seem to be in error, as would the report by Over and Churchill (1945:28) of Eutamias inhabiting "... thickets along the Little Missouri River of Harding County."
Females evidently bear but one litter annually (in late May) in northwestern South Dakota and young are weaned by the latter part of June. Females taken on May 15 and 19 carried embryos (five measuring 30 and three measuring 28, respectively). A lactating female with five placental scars was obtained on May 24, but eight adult females taken after June 23 previously had weaned young. Juveniles were collected on June 24 and 25. Testes of two adult males collected in mid-May measured 11 and 18, but males taken in summer had much smaller testes.
In late spring, most adult least chipmunks molt from the worn, drab-gray pelage of winter to a brighter, more tawny summer pelage, but molt in a few females, perhaps originally delayed by reproductive activity, continues well into the summer months. Of seven specimens taken between May 15 and 24, two (one male and one lactating female) were in an early stage of molt, whereas the remainder were in winter pelage. Nine specimens (four females and five males) taken in mid- and late June were molting, but two females collected then were in winter pelage, and three animals, two males and a female, had completed molt to summer pelage. One adult female taken on August 5 had yet to complete molt to summer pelage. In our material, the first indication of molt from winter to summer pelage appears on the top of the head and the cheeks. Thereafter, molt proceeds posteriorly over the shoulder region and more or less evenly along the back and sides. In two specimens, small patches of molt preceded the general molt line. Molt on the venter apparently begins after molt on the dorsum approaches completion, but we could discern no definite pattern; on four specimens, hair was being replaced on the venter in scattered patches.
An August-taken young of the year engaged in post-juvenal molt had new adult pelage in a vague hour-glass pattern in the dorsal trunk region as well as on the cheeks and anterior part of the head. It was actively molting on top of the head, between the ears, over the shoulders, laterally behind the front feet, and along the sides, and had old pelage on the rump. Ventrally, the new adult pelage was evident only along the midline.
One adult male examined for ectoparasites harbored a tick, Dermacentor andersoni Stiles, and fleas, Monopsyllus eumolpi Rothschild.
Spermophilus tridecemlineatus pallidus J. A. Allen, 1874
Thirteen-lined Ground Squirrel
Specimens examined (22).—2 mi. N, 5 mi. W Ludlow, 5; 19 mi. N, 1 mi. E Camp Crook, 2; 2 mi. S, 2 mi. W Ladner, 1; 6-1/2 mi. N, 2 mi. W Camp Crook, 1; 1/2 mi. W Reva, 3; 4 mi. S, 1/2 mi. W Reva, 1; 6 mi. W Reva, 7; 15 mi. S, 4 mi. W Reva, 1; 7 mi. S, 4-1/2 mi. E Harding, 1.
Ground squirrels are common in areas of short grass; we observed them most frequently along roadways and fencerows in otherwise overgrazed flats. Many of our specimens were shot or taken in break-back traps baited with rolled oats in just such situations.