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Sorex palustriswater shrew

By Ma Carmen

Geographic Range

Water shrews, Sorex palustris, are found throughout Alaska and Canada to the northern mountain regions of the United States. (Beneski and Stinson, 1987)

Habitat

Water shrews are common inhabitants of northern forests. As the name would suggest, water shrews are often found around streams and other aquatic habitats. Areas with high humidity surrounded by heavy vegetation, logs and rocks are preferred. (Beneski and Stinson, 1987)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Water shrews are relatively large shrews with males tending to be longer and heavier than females. The total length of a water shrew can range between 130 and 170 mm, and the weight ranges from 8 to 18 grams (Wilson and Ruff,1999). Although the colour of the pelage may be variable, it is generally black or grey-black dorsally and a silvery-grey ventrally, but appears more black in the winter and becomes more brown in the summer. Water shrews, as a member of the long tailed shrews, can have tails varying from 57 to 89 mm in length (Wilson and Ruff, 1999). The tail is bicoloured, dark above and white or grey below or occasionally concoloured (Beneski and Stinson, 1987). The hind feet (18 to 21 mm) are larger than the fore feet and have a trim of 1 mm long stiff hairs (fibrillae) on the toes and the inner and outer sides of the feet (Peterson, 1966). A fringe of smaller stiff hairs is also found on the fore feet. The skull of the water shrew is large (21 to 23 mm and width 10 to 11 mm) with a dental formula of 1/1 5/1 1/1 3/3 = 32; the fourth upper unicuspid is characteristically smaller than the third. (Beneski and Stinson, 1987; Wilson and Ruff, 1999)

  • Sexual Dimorphism
  • male larger
  • Range mass
    8 to 18 g
    0.28 to 0.63 oz
  • Range length
    130 to 170 mm
    5.12 to 6.69 in

Reproduction

The breeding season is usually from December to September (Nagorsen, 1996). In one breeding season, two to three litters may be produced, each litter ranging from 3 to 10 offspring (Wilson and Ruff, 1999). Three weeks are devoted to gestation and then birth takes place in spring or summer (van Zyll de Jong, 1983; Nagorsen, 1996). Males reach sexual maturity in the winter following birth. During this time, their body weight increases and their testes become enlarged. The testes of sexually mature males can weigh more than 110 mg (Conaway, 1952). Most females, like males, attain sexual maturity in winter and breed in late winter or early spring, but there have been reports that some become reproductively active during their first summer. (Beneski and Stinson, 1987; Conaway, 1952; Nagorsen, 1996; Wilson and Ruff, 1999)

  • Breeding interval
    Water shrews produce two to three litters per breeding season.
  • Breeding season
    The breeding season is usually from December to September.
  • Range number of offspring
    3 to 10
  • Average number of offspring
    5
    AnAge
  • Average gestation period
    3 weeks
  • Average gestation period
    23 days
    AnAge
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    90 days
    AnAge

Like all female mammals, water shrew mothers provide their young with milk after they are born.

  • Parental Investment
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Water shrews are short-lived. The typical life span of a water shrew is about 18 months. (Nagorsen, 1996; Wilson and Ruff, 1999)

  • Average lifespan
    Status: wild
    18 months

Behavior

Water shrews are solitary creatures, active throughout the day and night. Their activity patterns are characterized by two periods; one between sunset and 2300 h, the second occurs one hour prior to sunrise (Sorenson, 1962). For every 30 minutes of activity, the shrew spends the next hour resting (van Zyll de Jong, 1983).

When active, water shrews dive and swim in water to forage for food. Water shrews can control their own metabolic demands so that they can dive year-round, even in winter-cold bodies of water (Boernke, 1977). Each dive can last from 31.1 to 47.7 seconds (Beneski and Stinson, 1987). In water, the fur is lined with a layer of air that reduces their heat loss by 50% (Calder, 1969) as well as make them buoyant. Therefore, when water shrews swim or dive, they must paddle vigorously to keep from floating to the surface. The hind feet, and the stiff hairs on them, propel them through the water. Immediately after swimming, water shrews dry off their fur using the hind feet. Besides swimming, some water shrews have been seen walking on the surface of water (Jackson, 1928). It has been suggested that water shrews can walk on water because they can trap air bubbles in the stiff hairs of their feet (Jackson, 1928).

Nests of water shrews are usually about 8 cm in diameter and are either new nests or reconstructions of old nests built from dried vegetation in tunnels or under hollow logs. Water shrews dig their own tunnels by digging with the fore feet and throwing out soil with their hind feet. New nests are built using their feet and legs to form a depression and the walls of the nest shaped with the muzzle (Nagorsen, 1996).

Water shrews are aggressive and fighting is common between conspecifics. Males and females are equally likely to fight (Sorenson, 1962). Most encounters are short but may be intense. Encounters between two individuals usually start off with each emitting high pitched squeaks followed by standing on their hind legs to expose their light-coloured bellies. If neither shrew retreats after these displays, they will begin to slash each other with their teeth as they wrap up into a tight ball. Head and tail injuries often occur (Sorenson, 1962). These fights have not been proven to be of a territorial nature. (Beneski and Stinson, 1987; Boernke, 1977; Calder, 1969; Jackson, 1928; Nagorsen, 1996; Sorenson, 1962; Wilson and Ruff, 1999)

Communication and Perception

Sensory abilities of water shrews are not well understood. The vibrissae and the muzzle are thought to serve the purpose of locating prey (Sorenson, 1962). During explorations they release continuous high pitched sounds. This has led people to believe that water shrews echolocate (Sorenson, 1962). Distinguished by the strong, sometimes nauseating odor they emit, water shrews are believed to have a well-developed sense of smell. These odors have been proposed to serve to attract mates or for species recognition (Hamilton, 1940). (Sorenson, 1962)

Food Habits

Water shrews are predominantly insectivores. Diving to the bottoms of streams or other water habitats, they forage for aquatic insects, especially for the larvae and nymphs of caddisflies, crane flies, mayflies, and stoneflies and occasionally for small fish (van Zyll de Jong, 1983). Besides aquatic animals, they will also feed on land for flies, earthworms, snails, fungi and green vegetation (Wilson and Ruff, 1999). Once in possession, the food is held by the fore feet and torn to pieces using the teeth through upward thrusting of the head (Sorenson, 1962). Water shrews can live without food for up to 3 hours, but captive shrews have been found to feed almost every 10 minutes (Nagorsen, 1996). The amount of food required by a water shrew has been estimated to be 0.95 g/day. (Nagorsen, 1996; Sorenson, 1962)

  • Animal Foods
  • fish
  • insects
  • mollusks
  • terrestrial worms
  • Other Foods
  • fungus

Predation

Water shrews dive and swim to escape from predators like garter snakes, hawks, owls and weasels. (Wilson and Ruff, 1999)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Water shrews are important predators of the insects on which they feed, and they are an important food source for the predators listed above. (Whitaker and Hamilton, 1998)

Economic Importance for Humans: Negative

The water shrew has no known negative effects on humans.

Conservation Status

Water shrews are widespread but rarely captured. (Wilson and Ruff, 1999)

Other Comments

The name Sorex palustris comes from the Latin word soric meaning "shrew-mouse" and paluster for "marshy". (Beneski and Stinson, 1987)

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Ma Carmen (author), University of Toronto.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Beneski, J., D. Stinson. 1987. Sorex palustris. Mammalian Species, 296: 1-6.

Boernke, W. 1977. A comparison of arginase maximum velocities from several poikilotherms and homeotherms. Comp. Biochem. Physiol., 56B: 113-116.

Calder, W. 1969. Temperature relations and under water endurance of the smallest homeothermic diver, the water shrew. Comp. Biochem. Physiol., 30A: 1075-1082.

Conaway, C. 1952. Life history of the water shrew (Sorex palustris). Amer. Midland Nat., 48: 219-248.

Jackson, H. 1928. A taxonomic review of the American long tailed shrews. N. Amer. Fauna, 51: 1-238.

Nagorsen, D. 1996. Opossums, Shrews of British Columbia. British Columbia: Royal British Columbia Museum.

Sorenson, M. 1962. Some aspects of water shrew behavior. Amer. Midland Nat., 68: 445-462.

Whitaker, J., W. Hamilton. 1998. Mammals of the Eastern United States. New York: Cornell University Press.

Wilson, D., S. Ruff. 1999. Water shrew, Sorex palustris. Pp. 38-39 in The Smithsonian Book of North American Mammals. Vancouver: UBC Press.

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