Mountain water shrews range over much of Canada and in mountainous areas of the western United States extend south to Arizona. The subspecies found in Washington ranges over all of the western United States.
The mountain water shrew is primarily a mammal of the Hudsonian and Canadian life-zones. It sometimes descends to the Transition Life-zone along clear, cold streams where conditions are similar to those in the Canadian Life-zone.
The favored habitats of the mountain water shrew are the clear, cold streams of the alpine cirques and gushing streams on the mountain sides. In the pools and waterfalls, and among the rocks and mosses that border them, the larvae of aquatic insects, upon which the mountain water shrew feeds, are abundant. [Svihla] (1934: 45) observed that the fur of a swimming water shrew gathered air bubbles and "it had difficulty in forcing its way down to the bottom [of an aquarium]. On reaching the bottom it literally stood on its long flexible nose which was thrust into the sand and debris, searching for food, its feet kicking rapidly in order to maintain this position. A change in direction was brought about by a twist of the body. To come to the surface again it merely stopped kicking and immediately rose like a cork." The buoyancy of the water shrew allows it to float in the water, like a duck. [Jackson] (1928: 9) observed a water shrew run across the surface of a small pool. Near Stevens Pass a water shrew dashed from under a stone and ran, did not swim, across the surface of a small, deep pool to escape in a burrow on the other side. According to [Jackson], an air bubble held in each foot supports the shrew on the surface of the water. A mountain water shrew observed at Shovel Creek, Ferry County, was as agile on land as any other species of shrew. In summary, water shrews are able to swim, dive, float like a duck, and walk on the surface of the water as well as walk on land.
The food of the mountain water shrew includes snails, leeches, and the larvae of aquatic insects. Mice caught in traps are sometimes eaten by water shrews. [Svihla] (loc. cit.) found a captive water shrew unable to capture pollywogs and minnows kept in the same aquarium.
Sorex bendirii ([Merriam])
Bendire water shrew
Description.—The Bendire water shrew is similar in form of body to the cinereous shrew but possesses a more stocky body which, with the head, measures about 3-1/2 inches long; the tail is about 2-3/4 inches long. The Bendire water shrew closely resembles also the mountain water shrew but has a longer body and shorter tail. The upper parts are blackish in color, not lightly frosted with gray hairs. The hind feet lack the fringe of stiff, curved bristles characteristic of the mountain water shrew. The underparts are black in the race S. b. bendirii. In the race albiventer the throat is blackish but the abdomen is pale gray tinged with brownish.
Fig. 32. Distribution of the Bendire water shrew and the pigmy shrew in Washington. A. Sorex bendirii bendirii. B. Sorex bendirii albiventer. C. Microsorex hoyi washingtoni.