Geographic Range
Water shrews,
Sorex palustris
, are found throughout Alaska and Canada to the northern mountain regions of the United
States.
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.
- 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.
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
- Sexual Dimorphism
- male larger
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- viviparous
Like all female mammals, water shrew mothers provide their young with milk after they are born.
- Parental Investment
-
pre-fertilization
-
protecting
- female
-
protecting
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-weaning/fledging
-
provisioning
- female
-
protecting
- female
-
provisioning
Lifespan/Longevity
Water shrews are short-lived. The typical life span of a water shrew is about 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.
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).
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.
- Primary Diet
- carnivore
- 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.
- 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.
Economic Importance for Humans: Negative
The water shrew has no known negative effects on humans.
Conservation Status
Other Comments
The name
Sorex palustris
comes from the Latin word
soric
meaning "shrew-mouse" and
paluster
for "marshy".
Additional Links
Contributors
Allison Poor (editor), University of Michigan-Ann Arbor.
Ma Carmen (author), University of Toronto.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- forest
-
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
- riparian
-
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
- 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.
- 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.
- 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).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- natatorial
-
specialized for swimming
- diurnal
-
- active during the day, 2. lasting for one day.
- nocturnal
-
active during the night
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- solitary
-
lives alone
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- 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.
- carnivore
-
an animal that mainly eats meat
- insectivore
-
An animal that eats mainly insects or spiders.
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.