Animal Diversity Web

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)

• Biogeographic Regions
• nearctic
  • native

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)

• Habitat Regions
• temperate
• terrestrial

• Terrestrial Biomes
• forest

• Aquatic Biomes
• lakes and ponds
• rivers and streams

• Other Habitat Features
• riparian

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)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• 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)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous

• 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)

• Key Behaviors
• terricolous
• natatorial
• diurnal
• nocturnal
• motile
• sedentary
• solitary

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)

• Communication Channels
• acoustic
• chemical

• Perception Channels
• tactile
• acoustic
• chemical

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)

• Primary Diet
• carnivore
  • insectivore

• 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

• Known Predators

  • garter snakes (Thamnophis)
  • hawks (Accipitridae)
  • owls (Strigidae)
  • weasels (Mustela)

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)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

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.

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.