Montana Field Guide

Like other members of the genus Sorex, the snout is long and pointed, and the eyes are small. The dorsal pelage is dark brown to dark gray, and the ventral pelage is silvery-gray. The tail is bicolored, olive-brown above and hazel-brown below. The skull has 32 teeth (dental formula: I 3/1, C 1/1, P 3/1, M 3/3); the 5 upper teeth with single cusps that are present posterior to the first incisor are termed the unicuspids (U), and include 2 incisors, 1 canine, and 2 premolars. The tine on the medial edge of the first incisor is long, acutely pointed, and set within the pigmented area; U3 is as large or larger than U4. Ranges of external measurements (in millimeters) are: total length 77 to 95, tail length 28 to 38, hind foot length 7 to 11, ear length 8 to 11, weight 2.1 to 4.1 grams (Cornely et al. 1992, Verts and Carraway 1998). Published cranial measurements (in millimeters) are: condylobasal length 13.8 to 15.1, palatal length 5.4 to 5.8, cranial breadth 7.0 to 7.2, interorbital breadth 2.9 to 3.1, maxillary breadth 3.8 to 4.2, dentary length 5.6 to 6.7, length of mandibular tooth row (C1-M3) 3.8 to 4.2.

Some Montana specimens (n = 14) exceed some reported values: condylobasal length 13.5 to 14.6, palatal length 5.4 to 6.2, cranial breadth 7.0 to 7.5, interorbital breadth 2.4 to 2.6, maxillary breadth 4.0 to 4.2, dentary length 5.9 to 6.3, length of mandibular tooth row (C1-M3) 4.0 to 4.2 (Hoffmann et al. 1969, Hendricks and Roedel 2002).

Preble's Shrew is small, even for a shrew. Other than its small body size, Preble's Shrew is diagnosed by cranial characteristics. A combination of a medial tine on I1 that is present within the zone of pigmentation, U3 as large or larger than U4, condylobasal length usually less than 15.1 millimeters, palatal length less than 5.8 millimeters, length of dentary less than 6.5 millimeters, length of mandibular tooth row (C1-M3) usually less than 4.1 millimeters, and height of coronoid process less than 3.3 millimeters (Junge and Hoffmann 1981, Carraway 1995).

No information is available on movements in Montana, but based upon information from other locations, the species is considered non-migratory; apparently only local movements are made.

Most Preble's Shrews in Montana have been captured in sagebrush-grassland habitats (Hoffmann et al. 1969, Foresman 2012, Hendricks and Roedel 2002), sometimes in openings surrounded by subalpine coniferous forest. They have been taken in Beaverhead County in stabilized sandhills habitat of about 40 to 60% vegetation cover, dominated by grasses (Stipa comata, Festuca idahoensis, Agropyron dasystachyum) and shrubs (Artemisia tridentata, A. tripartita, Chrysothamnus nauseosus, C. viscidiflorus, and Tetradymia canescens), with isolated dense patches of Opuntia fragilis present (Hendricks and Roedel 2002). Preble's Shrew was also present at two other grazed sites (in Beaverhead and Powell counties) dominated by medium-stature (0.5 to 1.5 meters tall) sagebrush; at both sites, sagebrush cover was about 25% (Paul Hendricks, unpublished data).

Throughout its range, the Preble's Shrew occupies a variety of habitats, including arid and semiarid shrub-grass associations, openings in montane coniferous forests dominated by sagebrush, willow-fringed creeks and marshes, bunchgrass associations, sagebrush-aspen associations, sagebrush-grassland, oak chaparral, open ponderosa pine-Gambel oak stands, and alkaline shrubland (Williams 1984, Ports and George 1990, Cornely et al. 1992, Long and Hoffmann 1992, Kirkland and Findley 1996, Verts and Carraway 1998).

The bulk of Preble's Shrews captured have come from arid habitats, often in the immediate or nearby presence of sagebrush. In southwestern Wyoming, individuals were captured in sagebrush-steppe: islands of Artemisia tridentata, Purshia tridentata, and Amelanchier utahensis more than 30 centimeters tall surrounded by large expanses of Artemisia less than 30 centimeters tall (Kirkland et al. 1997). In southern British Columbia, Preble's Shrews were captured in lightly to moderately grazed grassland patches surrounded by scattered stands of Douglas-fir (Pseudotsuga menziesii) or ponderosa pine. Big sagebrush, common snowberry (Symphoricarpos albus), or antelope bitterbush (Purshia tridentata) about 1 to 2 meters in height formed dense shrub cover of 30 to 80% (Nagorsen et al. 2001); cheatgrass (Bromus tectorum) was sometimes dominant, and the nearest standing water to trap sites was 350 to 2300 meters distant.

The diet of Preble's Shrew has not been described or the subject of study, but it probably resembles other cinereus-group shrews, feeding on insects and other small invertebrates (worms, molluscs, centipedes, etc.). Its relatively low bite force suggests that it feeds on soft-bodied prey (Cornely et al. 1992, Verts and Carraway 1998). The diet in Montana has not been reported or studied.

Little is known about this shrew, but it is probably active all year. It has been captured in spring and late summer in southwestern Wyoming (Kirkland et al. 1997), in summer and during fall to spring in British Columbia (Nagorsen et al. 2001), summer and fall in Nevada (Ports and George 1990), and mid-winter in Utah (Tomasi and Hoffmann 1984). Collection records from Montana range from mid-February to early November.

Other small mammal associates of Preble's Shrew across its range include Sorex cinereus, S. haydeni, S. merriami, S. monticolus, S. nanus, and S. vagrans (Ports and George 1990, Cornely et al. 1992, Kirkland and Findley 1996, Kirkland et al. 1997, Nagorsen et al. 2001). Preble's Shrew has been collected in Montana in close association with Sorex cinereus, and S. monticolus (Hendricks and Roedel 2002).

Vital statistics, measures of population trends, and estimates of population density are not available; at many of the locations where several species of shrews have been captured in association with Preble's Shrew, it is always one of the less abundant species (Ports and George 1990, Kirkland et al. 1997, Nagorsen et al. 2001, Hendricks and Roedel 2002). Predators of Preble's Shrew have not been reported.

The reproductive biology in Montana has not been studied, and in general, the reproductive biology of Preble's Shrew is largely unknown (Cornely et al. 1992). In a sample of 26 specimens from southeastern Oregon collected in June and July, five adult females contained developing embryos: two with 3 embryos, two with 5, and one with 6; mean = 4.4 embryos (Carraway and Verts 1999); all had elongated nipples and extensive mammary tissue suggesting they had produced at least one litter earlier. Four juvenile females exhibited no evidence of reproductive activity. For 16 males, testis size in 15 individuals was either less than 2.0 cubic millimeters (nonreproductive, captured in the year of birth) or more than 16.0 cubic millimeters (reproductive, from older cohorts); one male with intermediate testis size had little wear on I1, indicating it may have just reached sexual maturity. These data suggest that at least two litters were produced before the June and July pregnancies.

No management measures have been enacted for Preble's Shrew in Montana. However, alteration or removal of sagebrush through fire, herbicides, or mechanical methods, may impact local populations (Hendricks and Roedel 2001). Measures taken to protect a diversity of size and cover classes of sagebrush will likely contribute to the conservation of Preble's Shrew. Surveys for Preble's Shrews can provide the basis for development of conservation protocols by determining its full distribution in Montana, the array of habitats in which it occurs, its relative abundance in different habitats, and, if properly designed, an idea of how different habitat disturbances affect this rare shrew.