WILDLIFE DIVERSITY NOTEBOOK: The Northern Water Shrew
Common Name: Northern Water Shrew
Scientific Name: Sorex palustris punctulatus (SORE-eks pah-LUS-tris PUNK-two-LATE-us)
Status Considered a “Species of Concern” by the United States Fish and Wildlife Service and a “Vertebrate Species of Concern” in West Virginia
West Virginia Status: Water shrews are known from 18 localities in five counties in the high mountain region of West Virginia
Description: The water shrew is the largest North American member of its genus, Sorex, the longtail shrews. It typically attains a total length of 6.1 inches (15.5 centimeters). The tail of this shrew commonly reaches 2.7 inches (7.0 centimeters), approximately 40 percent of its total body length. Its fur is dark gray on top and slightly lighter on the belly. The tail of the water shrew is bicolored-light on the bottom and darker on top. As with all shrews, the water shrew has a compact body, with short legs and a pointy snout. Its eyes are quite small and its ears are hardly distinguishable under the dense fur. The water shrew, unlike other longtail shrews, has very large hind feet that feature fringe hairs and are slightly webbed between the third and fourth toes. These adaptations enable this shrew to move efficiently through streams and pools.
Habitat: The Northern water shrew is usually associated with high elevation forests. Such forests tend to feature yellow birch, beech, red spruce, red maple and hemlock trees in the overstory and dense understories of rhododendron, mountain laurel or other shrubs. This animal is typically found along mountain streams characterized by cut banks, rocks, fallen logs, and abundant moss and leaf litter. Clear, relatively pure water that harbors an abundance of aquatic insects seems to be an essential part of its habitat.
Threats: And Prospects Because of their dependence on aquatic habitats, water shrews are especially vulnerable to declines in water quality. Stream pollution, acidification and sedimentation may have negative impacts on the aquatic invertebrates on which water shrews depend for food. Channelization and stream bed manipulations can reduce the number of feeding pools, runways and nest sites, as can the removal of fallen logs and boulders. Other threats to this secretive animal are loss of habitat to residential and recreational development, and stream side logging.
In spite of having only 18 known records from West Virginia, the water shrew seems to be holding its own in the Mountain State. Because of their high metabolism, water shrews often die when caught in live traps, so surveys are limited to reduce impacts on their populations.
Because of their small size and secretive habits, the range and abundance of water shrews are probably underestimated in the state. There appear to be many areas of good habitat remaining in the state’s higher elevations. Sound logging practices, coupled with improved water quality in formerly acidified streams should help assure the water shrew’s continued presence among West Virginia’s fauna.
Landowners can help the water shrew through the following streamside management practices: preventing water pollution, controlling erosion and sedimentation, and maintaining shade and natural debris along streams.
Range: The northern water shrew occupies a range that includes most of Canada, New England, the Appalachian Mountains, the upper Midwest and the mountainous regions of the western United States. However, the subspecies found in the Mountain State, Sorex palustris punctulatus, occurs in only six mid-Appalachian states. In West Virginia, the water shrew has been found in Preston, Tucker, Randolph, Pendleton and Pocahontas counties at locations over 2,000 feet in elevation.
Life History: Water shrews start their breeding activities in the early spring. They may have several broods of four to eight young by September. The females of early litters may reach maturity in time to have their own litters later that same summer, but generally they do not reproduce until the following year. The gestation period for this species is approximately 21 days.
Water shrews use dried moss to build nests in underground burrows under rocks and logs or in stream banks. They are active year round and will leave their burrows in winter to forage when weather permits. Life expectancy of this animal probably does not exceed two years in the wild.
Diet: The water shrew subsists primarily on aquatic insects, their larvae and crustaceans. However, it has also been known to consume terrestrial invertebrates—snails, slugs, spiders, beetles, centipedes and worms—and small fish, fish eggs, as well as amphibians and their larvae. Shrews have very high metabolic rates and thus spend a large portion of their active hours searching for food. The water shrew can consume over half of its weight in food daily (approximately 100 insects.)
Additional Comments: There are several subspecies of the northern water shrew in the Eastern United States. If you hear the terms southern, Appalachian or West Virginia water shrew, these all refer to the southern subspecies of the northern water shrew, the one that occurs in West Virginia.