Montana Field Guide

A large, semiaquatic, blackish-gray shrew with a long bicolored tail and large hind feet fringed with short stiff hairs. Total length is 14 to 16 cm (5.5 to 6.3 inches) including a 6 to 8 cm (2.4 to 3.1 inch) tail. The dense fur is glossy blackish gray above and paler or silvery beneath. Middle toes of hind feet (18 to 20 mm) are partially webbed. For good descriptions and illustrations see Burt and Grossenheider (1976), Godin (1977), Hall (1981), Beneski and Stinson (1987), Clark and Stromberg (1987), and Merritt and Matinko (1987). The sexes are similar in size and color. Sexually active males (February to September) have prominent dermal glands on each side between fore and hind legs. They show in S. p. navigator as an 8-mm oval patch of white hair (Conaway 1952). Immatures are similar in color to adults. The skull is large and heavy for a shrew, generally more than 19.5 mm long in S. p. punctulatus. The first two unicuspid teeth are noticeably larger than the next two (Banfield 1974), the third unicuspid is smaller than the fourth (Godin 1977), and the fifth is greatly reduced (Pagels 1986). For comparative illustrations of shrew dentition, see Conaway (1952), Banfield (1974), Churchfield (1990). The teeth of North American shrews show some reddish brown pigmentation. Scats of Western Water Shrews are quite distinctive, black and granular in structure, being full of remains of invertebrate exoskeletons. They are often deposited in middens on the banks of streams, in surface burrows, at burrow entrances, in the lee of rocks at the stream edge, or even sometimes quite prominently on the tops of stones (Churchfield 1990). Western Water Shrew hairs are roughly H-shape in cross section, with inner surfaces deeply ridged (see illustration in Churchfield 1990).

Western Water Shrew was previously known as the Northern Water Shrew (S. palustris), but recent analysis of genetic differences across this species range provided evidence that the species should be split into three species with the Western Water Shrew occuring in Montana.

Stiff hairs along the sides of the hind feet are found only in the Western Water Shrew and the Pacific Water Shrew (Sorex bendirii). The latter, a Pacific Northwest species, differs in being slightly larger (8.9 to 9.7 cm, 3.5 to 3.8 inches, body length) and dark brown rather than blackish-gray (Burt and Grossenheider 1976). See Carraway (1995) for a key to western North American soricids based primarily on dentaries.

Non-migratory.

In streamside habitat in coniferous forests, particularly in or under overhanging banks or crevices; prefer good cover (Conaway 1952). However, also found in seasonal streams and small seeps (Kinsella 1967). Also above timberline (Hoffmann and Pattie 1968).

Aquatic insect larvae, also some vegetable matter, Oligochaetes, other shrews, arachnids, and small fish (Conaway 1952). Captures in small seeps (Kinsella 1967) imply dietary flexibility.

A captive specimen required cold water. Used smell and tactile senses to capture fish. Fur would become soaked within several minutes immersion, and specimen dried itself by working fur with hind feet (Conaway 1952).

Males produce sperm December to August. Pregnant or lactating females found February to August. Several litters/season, around 6 young/litter. Males reproductively mature 2nd year, females 1st year but often do not produce litter until 2nd year.