Water Shrew(Sorex palustris Cope)
From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry. 216pp.
Description: This grey-black to blackish-brown shrew with a pointed, down-drooping nose averages 147-157 mm (5.8-6.2 in) in length, and is the longest of the Adirondack shrews. It weighs 10-17 g (0.35-0.60 oz), slightly less than the largest short-tailed shrew. The water shrew’s weight and long tail (67-71 mm, 2.6-2.8 in) (as long or longer than the combined head-body length) distinguished it from all other Adirondack shrews. A fringe of stiff hairs along the margins of the toes, especially those of the broad hind feet, and the partially webbed hind toes are unique features.Range and Habitat: Water shrews occur from southern Alaska south and east across Canada, parts of the western, northern, and northeastern U.S. The range coincides with the boreal and mixed forests. Records of Adirondack specimens indicate this species is present throughout the park from elevations of at least 177 m to 1189 m (580-3900 ft). Water, as the common name suggests, is the necessary prerequisite for this shrew. Bogs, the edges of lakes and ponds, marshes, shrub swamps, rivers, and streams - even if only intermittent - provide suitable habitat. Fast-flowing cold streams may harbor the largest populations.
Water shrews build their small nests of moss or other plant materials among rocks, logs, and tree roots, or in short tunnels 10-12 cm (4-5 in) which they excavate by loosening soil particles with their front feet and pushing them backwards with their hind feet. They also live in the outer walls of beaver lodges and muskrat huts.
Food and Feeding Behavior: Water shrews share the prodigous appetites of their relatives, and require large amounts of food each day. For example, 1 10g (0.4 oz) captive consumed 10.3 g (0.4 oz) of food in one 24 hour period. Insects, particularly aquatic species, e.g. larvae and nymphs of caddis flies, mayflies, and stoneflies, form the major portion of the diet. Other aquatic invertebrates such as snails and planarians, carrion, fungi, and vertebrates or their eggs make up a lesser part of the diet. Water shrews routinely forage underwater rooting among bottom debris for aquatic insects or relying on their sight to locate and outswim mobile prey. These shrews dive frequently but briefly, submerging for less than a minute. They carry captured prey from the water in their jaws and sit on a nearby perch to feed.
Activity and Movement: This species is active at all times of the year and throughout the day with more activity occurring at dawn and dusk during a 24 hour period. Periods of rest of about 60 minutes alternate with bouts of activity lasting 30 minutes. Water shrews run or walk on land, wandering 30.5 m (100 ft) from water. In the water they float, dive, or swim. They paddle with all four feet when swimming. Their most remarkable means of locomotion is running upright on their hind feet across the surface of quiet water, crossing distances of at least 1.5 m (5 ft).
Reproduction: The reproductive biology of water shrews is poorly documented, especially for eastern populations. The breeding season probably begins in February or March and extends into August. Litter size is 5-7. Females may bear 2 or 3 litters per year. The duration of gestation and lactation is unknown. Longevity is 18 months.
Predators: Garter snakes, brook trout, and weasels are known predators. Larger carnivorous mammals, other fish, and snakes, hawks, and owls are suspected predators.
- Social System - This facet of the natural history of the species is unknown. Adults are usually solitary and either flee or respond aggressively when encountering another water shrew. Aggressive individuals squeak continuously, rise up on their hind legs, and attempt to bite an opponent. Actual contact and fighting may follow until one leaves.
- Communication - As is true for all shrews, lateral skin or flank glands enlarge during the breeding season and produce chemicals which are likely clues to species recognition, sexual status, and perhaps even individual identity. These substances or scents may also function to space individuals. Vocalizations are an obvious form of signaling; other means await study.
Brown, L.N. 1967. Ecological distribution of six species of shrews and comparison of sampling methods in the central Rocky Mountains. Journal of Mammalogy, 48:617-623.
Conaway, C.H. 1952. Life history of the water shrews (Sorex palustris navigator). American Midland Naturalist, 48:219-248.
Wrigley, R.E., J.E. Dubois, and H.W. Copland. 1979. Habitat, abundance, and distribution of six species of shrews in Manitoba. Journal of Mammalogy, 60:505-520.