Mammals of Northwestern South Dakota Part 3

~Reithrodontomys megalotis dychei~ J. A. Allen, 1895

Western Harvest Mouse

_Specimens examined_ (27).--NE 1/4 sec. 22, R. 1 E, T. 23 N, 1; 4 mi. S, 7 mi. W Ladner, 3; 2 mi. N, 5 mi. W Ludlow, 7; 1/2 mi. W Reva, 14; 10 mi. S, 5 mi. W Reva, 1; 14 mi. S, 4 mi. W Reva, 1.

The western harvest mouse was taken commonly in stands of tall gra.s.ses and forbs, particularly along roadways and fencerows. Occasional individuals were trapped in areas of mixed shrubs and gra.s.ses. Four pregnant females taken in late June carried the following number of embryos (crown-rump lengths in parentheses): seven (4), six (5), six (10), five (4). Three adult males taken in the same period had testes that measured 7, 7, and 8, whereas those of two May-taken males measured 12 and 6.

Molt from winter to summer pelage was in progress, from anterior to posterior, on both the dorsum and venter of many May- and June-taken animals. Some individuals had completed molt, or had but a small patch of winter pelage remaining on the rump, as early as the last week in June.

~Reithrodontomys monta.n.u.s albescens~ Cary, 1903

Plains Harvest Mouse

_Specimens examined_ (3).--2 mi. N, 5 mi. W Ludlow, 2; 1/2 mi. W Reva, 1.

This harvest mouse is uncommon in northwestern South Dakota, although the species probably occurs sparingly in upland gra.s.sy habitats throughout Harding County. Our specimens, along with one in the collections of the University of Michigan Museum of Zoology, not previously reported, from 11 mi. S Mandan, Morton Co., North Dakota, represent the northernmost known records of this mouse.

A young adult female, obtained on June 21, carried three embryos that measured 17 and was in summer pelage; an adult male taken on June 27 still was in a worn winter pelage.

At the locality 1/2 mi. W Reva, where traps were set in spa.r.s.e to relatively lush gra.s.sy areas along South Dakota Highway 20, the following small mammals were taken in the same trapline (or adjacent lines) in which one plains harvest mouse was captured: _Spermophilus tridecemlineatus pallidus_, _Reithrodontomys megalotis dychei_, _Peromyscus maniculatus nebrascensis_, _Microtus ochrogaster haydenii_, and _Microtus pennsylvanicus insperatus_.

~Peromyscus leucopus aridulus~ Osgood, 1909

White-footed Mouse

Seven adults of this woodland inhabitant were trapped along shrub-covered banks of the spring-fed stream and small impoundment in Deer Draw of the Slim b.u.t.tes (10 mi. S and 5 mi. W Reva). Deciduous trees grew in the bottom of the draw, but the slopes above supported ponderosa pine and juniper. No white-footed mice were found along the generally treeless tributaries of the Moreau and Grand rivers to the east of Slim b.u.t.tes nor were these mice found along the Little Missouri River or in likely-looking habitat in the North Cave Hills. The _P.

leucopus_ of Deer Draw likely represent, therefore, an isolated segment of a formerly much more broadly distributed population of white-footed mice on the Northern Great Plains in post-Wisconsin times. Other such populations may exist in Slim b.u.t.tes and perhaps elsewhere in the county. _Zapus hudsonius_ and _Microtus pennsylvanicus_ were trapped in Deer Draw in a.s.sociation with white-footed mice.

Females collected on June 15 and August 7 were lactating and one taken on June 20 contained six embryos that measured 15. Two males taken on June 2 had testes that measured 12 and 15. These two males and a lactating female taken on June 15 still were in winter pelage, whereas a non-breeding female obtained on June 15 and a male and female (pregnant) trapped on June 20 were in summer pelage or an advanced stage of molt to that pelage. A lactating female taken on August 7 was in summer pelage excepting that what definitely appeared to be new winter pelage was present on the head, cheeks, and below the ears, and molt was evident adjacent to these areas.

Selected average (and extreme) measurements of the seven adults from Deer Draw are: total length, 184.4 (175-199); length of tail, 77.4 (70-88); length of hind foot, 21.1 (20-22); length of ear, 16.7 (16-18); greatest length of skull, 27.8 (27.0-28.4); zygomatic breadth, 14.6 (14.0-14.9); least interorbital width, 4.1 (4.0-4.3); length of maxillary toothrow, 4.2 (4.0-4.4). Three males and two non-pregnant females weighed 34.9, 34.6, 30.5, 32.2, and 31.4 grams, respectively.

~Peromyscus maniculatus nebrascensis~ (Coues, 1877)

Deer Mouse

_Specimens examined_ (214).--19 mi. N, 1 mi. E Camp Crook, 5; 18 mi. N Camp Crook, 2; 2 mi. N, 5 mi. W Ludlow, 58; 4 mi. S, 7 mi. W Ladner, 14; 9 mi. N, 3 mi. W Camp Crook, 3400 ft., 3; 7 mi. N, 2-1/2 mi. W Camp Crook, 3300 ft., 2; NW 1/4 sec. 32, R. 1 E, T. 20 N, 4; 1/2 mi. W Reva, 2; SW 1/4 sec. 30, R. 7 E, T. 18 N, 5; 9 mi. S, 7 mi. W Reva, 3; 10 mi.

S, 5 mi. W Reva, 64; 14-15 mi. S, 4 mi. W Reva, 33; 2 mi. S, 5 mi. E Harding, 16; 7 mi. S, 4-1/2 mi. E Harding, 3.

The deer mouse is the most abundant and widespread small mammal in northwestern South Dakota. We took specimens in all terrestrial habitats, although the species was commonest in upland situations such as gra.s.sy fencerows, rocky areas, and hillsides supporting shrubs, juniper, or pine.

Adult mice in reproductive condition were taken in each month from May through August, although most of our information is for the months of May and June. In the last half of May, seven pregnant females carried an average of 5.0 (4-6) embryos that ranged in crown-rump length from 2 to 10; three others taken in the same period had six, six, and three recent placental scars, and another was lactating. Twenty-three males collected late in May had testes that measured 5 to 15 (average 10.2). In the last half of June, 19 females contained an average of 4.9 (2-7) embryos that ranged in size from 3 to 30 in crown-rump length, and two more were lactating; seven males obtained in the period June 15-25 had testes that averaged 8.7 (8-10).

Additionally, we took lactating females on July 6, July 7, and August 7, and two individuals with recent placental scars on August 5. Twenty adult males collected in the period July 6 to 18 had testes that averaged 9.3 (6-11.5), whereas those of two taken on August 4 and 5 measured 10 and 12, respectively. Young animals in juvenal pelage were captured in each month, May through August, the earliest being taken on May 20. The first female young of the year that was found carrying embryos was trapped on June 16.

Molt from winter to summer pelage is evident on some specimens taken as early as the latter part of May, but most individuals from that period and from the first part of June still retained winter pelage. By the last half of June, some mice had completed (or nearly so) the seasonal molt, but many retained at least some worn pelage of winter into the first week of July.

Two distinctive maturational pelages are seen in our material--juvenal and post-juvenal or subadult, which generally resembles adult pelage (of season) in texture but is duller of color. Collins (1918) for _P.

maniculatus_, Hoffmeister (1951) for _P. truei_, and Brown (1963) for _P. boylii_, among others, have described maturational pelages and sequence of maturational molts similar to those observed in our specimens.

Deer mice from Harding County clearly are referable to _P. m.

nebrascensis_ (rather than to the smaller and paler _P. m. luteus_, which occurs to the east and southeast), even though adults average somewhat paler than adults of typical populations of that subspecies. A tick of the _Ixodes ochotonae-angustus_ complex was obtained from one specimen.

~Onychomys leucogaster missouriensis~ (Audubon and Bachman, 1851)

Northern Gra.s.shopper Mouse

_Specimens examined_ (4).--NE 1/4 sec. 22, R. 1 E, T. 22 N, 2; 2 mi. N, 5 mi. W Ludlow, 1; 14 mi. S, 4 mi. W Reva, 1.

We found the gra.s.shopper mouse uncommon in Harding County. All four of the mice listed as examined were trapped in areas supporting sage and short gra.s.ses, with relatively little ground cover.

Three of our four specimens are immature--two males collected on May 31 (testes 10, 12) and a female taken on June 25. An adult male trapped on June 18 was in winter pelage, but molt was underway on the crown, between the ears, and over the upper back and shoulders.

~Neotoma cinerea rupicola~ J. A. Allen, 1894

Bushy-tailed Wood Rat

_Specimens examined_ (8).--2 mi. N, 5 mi. W Ludlow, 5; 12 mi. N Buffalo, 1 (USNM); 7 mi. N, 2-1/2 mi. W Camp Crook, 3300 ft., 1; 2 mi. S, 5 mi. E Harding, 1.

This woodrat is relatively uncommon, yet widely distributed, in northwestern South Dakota. The species probably occurs throughout the rocky areas in the hills and b.u.t.tes of Harding County, and also frequents abandoned or little-used buildings and feed stations for livestock. All of our specimens were trapped in rocky habitats, but in many such places we trapped unsuccessfully for _Neotoma cinerea_, even though some sign of its presence frequently was evident. Five of our seven specimens (all taken late in June or early in July) are young of the year in grayish pelage. An adult male trapped on July 14 had testes that measured 14.

Over and Churchill (1945:40) mentioned a specimen, which they referred to the subspecies _N. c. cinerea_, that "probably came from the Slim b.u.t.te area of Harding County." Visher (1914:89) recorded the species as "plentiful and general" in the county.

~Microtus ochrogaster haydenii~ (Baird, 1858)

Prairie Vole

_Specimens examined_ (40).--NE 1/4 sec. 22, R. 1 E, T. 23 N, 1; NW 1/4 sec. 15, R. 5 E, T. 22 N, 1; 2 mi. N, 5 mi. W Ludlow, 4; 4 mi. S, 7 mi.

W Ladner, 19; 1/2 mi. W Reva, 2; SW 1/4 sec. 30, R. 7 E, T. 18 N, 3; 10 mi. S, 5 mi. W Reva, 10.

The prairie vole is the most abundant of the three microtines that are known from Harding County. Our specimens came primarily from areas of relatively dense gra.s.ses, such as those found in stream bottoms and along fencerows. At two places, along a fencerow 1/2 mi. W Reva and in Deer Draw, 10 mi. S and 5 mi. W Reva, _Microtus ochrogaster_ and the meadow vole, _M. pennsylvanicus_, were trapped together.

Nine females taken late in May and in June carried an average of 4.4 (3-6) embryos that averaged 14.8 (4-25) in crown-rump length. Each of two lactating females taken in late May had six placental scars. Testes of seven adult males taken in May and June averaged 13.1 (12-16) in length.

~Microtus pennsylvanicus insperatus~ (J. A. Allen, 1894)

Meadow Vole

_Specimens examined_ (14).--1/2 mi. W Reva, 1; 10 mi. S, 5 mi. W Reva, 12; 7 mi. S, 4-1/2 mi. E Harding, 1.

This vole evidently is limited in Harding County to habitats of dense gra.s.s and forbs adjacent to water. We failed to trap the species in some areas that appeared to be suitable for occupancy.