CDC Logo

BC Conservation Data Centre: Species Summary


Sorex bendirii
Pacific Water Shrew

 
Scientific Name: Sorex bendirii (Merriam, 1884)
English Name: Pacific Water Shrew
 
Classification / Taxonomy
Scientific Name - Concept Reference: Wilson, D. E., and D. M. Reeder (editors). 1993. Mammal species of the world: a taxonomic and geographic reference. Second edition. Smithsonian Institution Press, Washington, DC. xviii + 1206 pp. Available online at: http://www.nmnh.si.edu/msw/.
Classification Level: Species
Species Group: Vertebrate Animal
Species Code: M-SOBE
Kingdom Phylum Class Order Family
Animalia Craniata Mammalia Eulipotyphla Soricidae
   
Conservation Status / Legal Designation
Global Status: G4 (Apr 2016)
Provincial Status: S2 (Feb 2024)
BC List: Red
Provincial FRPA list: Y (May 2004)  
Provincial Wildlife Act:
COSEWIC Status: Endangered (Apr 2016)
SARA Schedule: 1  -  Endangered (Jun 2003)
General Status Canada: 1 - At Risk (2005)
   
Ecology & Life History
General Description: See Nagorsen (1996).
Subspecies Comments: Three subspecies are recognized with S. b. bendirii the subspecies in BC (Hall 1981). Gene trees calculated by O'Neill et al. (2005) showed no evidence of distinct clades or groups consistent with these subspecies. O'Neill et al. (2005) speculated that the Fraser River could be a major barrier promoting genetic isolation among BC populations; they recommended a study of nuclear DNA (microsatellites) to assess genetic divergence among BC populations on the north and south sides of the river.
Identification Comments: Illustrated keys are in Nagorsen (1996, 2002). Large size, dark pelage, and fimbriated hind feet readily disinguish S. bendirii from other shrews in most areas of the lower mainland. However, in the Chilliwack Valley and north shore mountains this species could be confused with the morphologically similar American Water Shrew (Sorex palustris). Distinguishing these two species of water shrews requires an animal in the hand.
Global Reproduction Comments: Considering the entire range, the breeding season extends from late January to late August (Nagorsen 1996, Maser 1998). Gestation lasts about 3 weeks. Litter size is 3-7 (Nagorsen 1996, Maser 1998, Verts and Carraway 1998). Females produce probably 2-3 litters in a single season. Males and probably female do not breed in their first summer (Pattie 1969, Nagorsen 1996). Apparently, adults breed in only one season and live not more than about 18 months (see COSEWIC 2006).
Provincial Reproduction Comments: No reproductive data are avilable for BC. In Oregon the breeding season extends from February to August with litter sizes ranging from 5 to 7 (Maser et al.1984; Verts and Carraway 1998). Males do not breed in their first summer (COSEWIC 2006).
Provincial Ecology Comments: What little is known about the ecology of this shrew in BC was summarized in the 2006 COSEWIC report (COSEWIC 2006). The limited ecological data available for this shrew is mostly derived from studies done in the United States particularly Oregon. See Verts and Carraway (1998) for a review. In addition to research on habitat requirements and diet in BC, the interaction of this shrew with the American Water Shrew (Sorex palustris) in areas of sympatry such as the north shore mountains and Chilliwack Valley needs to be studied to assess the impact of competive exclusion on the ecology of S. bendirii.
Migration Characteristics:
(Global / Provincial)		 
    Nonmigrant:
    Local Migrant:
    Distant Migrant:
    Within Borders Migrant: 		Y / Y
N / N
N / N
na / N
Global Migration Comments: Harris (1984) estimated home range size at 1.09 hectares but did not provide the source of this estimate.
Provincial Mobility & Migration Comments: Nothing is known about the home range size and shape, daily movements, or dispersal movements of this species in any part of its range. Harris (1984) gave a home range estimate of 1.09 ha but with no explanation of how this was calculated. Using Harris' 1.09 ha value, Craig (2007) calculated that an elliptical-shaped home range would extend 167 m along a watercourse and a linear home range would extend ~ 400 m along a waterbody. The bar graphs in McComb et al. (1993) and Gomez and Anthony (1998) suggest that most Pacific Water Shrew activity is 0-50 m from water. Data for British Columbia are limited. Craig's (2007) conclusion that Pacific Water Shrew is usually captured within 25 m of water was based on a statement in the original COSEWIC report by Galindo-Leal and Runciman (1994) who cited the study by Zuleta and Galindo-Leal (1994) as their source. Yet, Zuleta and Galindo-Leal (1994) gave no information on distance from water for their 55 trap transects or their 3 Pacific Water Shrew captures. Dispersal distances are unknown but, McComb et al. (1993) captured this shrew in upland forests as far as 350 m from water.
Habitats:
(Type / Subtype / Dependence) 		Forest / Conifer Forest - Moist/wet / Facultative - frequent use
Other Unique Habitats / Estuary / Facultative - occasional use
Riparian / Gravel Bar / Obligate
Riparian / Riparian Forest / Obligate
Riparian / Riparian Herbaceous / Obligate
Riparian / Riparian Shrub / Obligate
Stream/River / Stream/River / Obligate
Wetland / Bog / Obligate
Wetland / Fen / Obligate
Wetland / Marsh / Obligate
Wetland / Swamp / Obligate
Global Habitat Comments: Sorex bendirii is primarily a riparian habitat specialist; often it is associated with dense wet forests (e.g., western red-cedar), marshes (e.g., areas with skunk cabbage), muddy forests and forest edges, or red alder stands and other vegetation adjacent to water (usually streams/springs) (Bailey 1936, Anthony et al. 1987, Nagorsen 1996, Verts and Carraway 1998, COSEWIC 2006), but sometimes it has been captured in upland forest (e.g., West 1991, McComb et al. 1993, Gomez and Anthony 1998). Generally it occurs in areas of coniferous or mixed forest with downed logs, sometimes in grassy habitats bordering ditches or sloughs (COSEWIC 2006); often, but not always, in mature stands (Bailey 1936, Anthony et al. 1987, Nagorsen 1996, Gomez and Anthony 1998, Verts and Carraway 1998, Lomolino and Perault 2001, COSEWIC 2006). This shrew is highly amphibious and readily swims and dives.
Provincial Habitat Comments: According to Craig and Vennesland (2007), ideal habitat in BC is riparian habitats associated with streams, creeks, and wetlands in mature coniferous (structural stages 5-7) or deciduous (structural stages 4-7) forests. A habitat model based on TEM data assigned habitat ratings to various habitats. There have been several recent captures in anthropogenic habitats such as drainage ditches. It is unknown if these captures are resident or dispersing animals. In BC, our understanding of habitat requirements is based on the three captures by Zuleta and Galindo-Leal (1994), historical museum records with poor location data, and a few recent captures with associated habitat information. Although a habitat model was developed by Craig (2007), the validity of her model and associated habitat ratings needs to be verified.
Food Habits: Invertivore: Adult, Immature
Global Food Habits Comments: Diet is primarily aquatic insects, slugs, snails, earthworms, and other small, usually soft-bodied invertebrates (Whitaker and Maser 1976, Verts and Carraway 1998), sometimes small fishes and salamander larvae, (see COSEWIC 2006).. Food may be captured on land or in water. Excess food may be cached.
Provincial Food Habits Comments: S. bendirii is a semi-aquatic shrew that can swim and dive under water. Diet of the BC population has not been studied. The only available data are anecdotal observations by Glen Ryder (pers. comm.) of this species feeding on salamander and dragonfly larve and a museum specimen from Peardonville that had "stomach contained water beetles, worms, insects" on its tag (COSEWIC 2006). A detailed diet study done in coastal Oregon revealed that about 25% of the food was aquatic. Major food types were insect larvae, slugs, snails, Ephemeroptera naids, unidentifed invertebrates, and earthworms (Whitaker and Maser 1976). Other prey taken in Oregon include salmon parr and a terrestrial snail (Haplotrema vancouverense) (Maser and Franklin 1974; COSEWIC 2006).
Global Phenology:
Global Phenology Comments: Activity occurs throughout the year.
Provincial Phenology:
(1st half of month/
2nd half of month)		 Jan: Active / Active
Feb: Active / Active
Mar: Active / Active
Apr: Active / Active
May: Active / Active
June: Active / Active
July: Active / Active
Aug: Active / Active
Sept: Active / Active
Oct: Active / Active
Nov: Active / Active
Dec: Active / Active
Provincial Phenology Comments: Similar to other species in the genus Sorex, S. bendirii would be expected to be incapable of entering daily or extended torpor and remain active throughout the year (McNab 1991).
Colonial Breeder: N
Length(cm)/width(cm)/Weight(g): 17/ / 16
Elevation (m) (min / max): Global: 
Provincial:  0 / 850
   
 
Distribution
Endemic: N
Global Range Comment: Range includes coastal lowlands of western North America, from southwestern British Columbia (Fraser Lowland Ecosection, eastward to the Chilliwack River and Harrison Lake; usually at elevations below 600 meters but up to 850 meters) to northwestern California (Nagorsen 1996, Galindo-Leal and Zuleta 1997). In British Columbia, S. palustris occurs at higher elevations (Nagorsen 1996).
 
Authors / Contributors
Global Information Author: Hammerson, G.
Last Updated: Jun 17, 2011
Provincial Information Author: D. Nagorsen
Last Updated: Mar 14, 2008
   
References and Related Literature
B.C. Ministry of Environment. Recovery Planning in BC. B.C. Minist. Environ. Victoria, BC.
Blood, D.A. 1995. Pacific Water Shrew. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. 6 pp.
British Columbia Ministry of Water, Land and Air Protection. 2004. Pacific Water Shrew in Accounts and measures for managing identified wildlife. British Columbia Ministry of Water, Land and Air Protection, Victoria, BC. 52pp.
Carraway, L. N. 1995. A key to Recent Soricidae of the western United States and Canada based primarily on dentaries. Occasional Papers of the Natural History Museum, University of Kansas (175):1-49.
Churchfield, S. 1992. The Natural History of Shrews. Cornell University Press, Ithaca, New York. 192 pp.
COSEWIC. 2006l. COSEWIC assessment and update status report on the Pacific water Shrew Sorex bendirii in Canada. COSEWIC Committee on the Status of Endangered Wildlife in Canada Ottawa. 28 pp.
Craig, V. 2007. Species account and preliminary habitat ratings for Pacific water shrew (Sorex bendirii) using TEM data v.2. Draft. Ecologic Research, Surrey. 42 pp.
Craig, V., and R. Vennesland. 2007. Best management practices guidelines for Pacific water shrew in urban and rural areas. Working Draft. British Columbia Ministry of Environment, Surrey. 39 pp.
Forest Practices Code. 1997. Pacific Water Shrew in Species and Plant Community Accounts for Identified Wildlife: Vol. 1. B.C. Minist. For. and B.C. Environ. 184pp.
Galindo-Leal, C., and J.B. Runciman. 1994. Status report on the Pacific Water Shrew, Sorex bendirii, in Canada. Unpubl. rep. submitted to Comm. on the Status of Endangered Wildl. in Can., Ottawa. 27pp.
George, S. B. 1988. Systematics, historical biogeography, and evolution of the genus Sorex. J. Mammalogy 69:443-461.
Gomez, D. M., and R. G. Anthony. 1998. Small mammal abundance in riparian and upland areas of five seral stages in Western Oregon. Northwest Science 72:293-302.
Hall, E. R. 1981. The mammals of North America. John Wiley and Sons, New York. 600+90 pp.
Harris, L. D. 1984. The fragmented forest. The University of Chicago Press, Chicago. 211 pp.
Jackson, H.H. 1928. A taxonomic review of the North Americanlong tailed shrews (genera Sorex and Microsorex). N. Amer. Fauna. 51:1-238.
Maser, C., and J. F. Franklin. 1974. Checklist of vertebrate animals of the Cascade Head Experimental Forest. U.S. Department of Agriculture, Forest Service, Portland, Oregon. 32 pp
Maser, C., B. R. Mate, J. F. Franklin, and C. T. Dryness. 1984. Natural history of Oregon coast mammals University of Oregon, Museum of Natural History, Eugene.
McComb, W. C., K. McGarigal, and R. G. Anthony. 1993. Small mammal and amphibian abundance in streamside and upslope habitats of mature Douglas-fir stands, western Oregon. Northwest Science 67:7-15.
McNab, B. K. 1991. The energy expenditure of shrews. Pages 35-45. in: J. S. Findley, T. L. Yates, (eds). The biology of the Soricidae. The University of New Mexico, Albuquerque.
Nagorsen, D. W. 1996. Opossums, shrews and moles of British Columbia. The mammals of British Columbia. Vol. 2. Royal British Columbia Museum Handbook. University of British Columbia Press, Vancouver. 169 pp.
Nagorsen, D.W. 1996. Opossums, Shrews and Moles of British Columbia. Royal B.C. Mus. Victoria, BC. 169pp.
Nagorsen, D.W. 2002. An identification manual to the small mammals of British Columbia. B.C. Minist. Sustainable Resour. Manage., and Minist. Water, Land and Air Prot., and Royal B.C. Mus., 153pp.
O'Neill, M.B., D.W. Nagorsen, and R.J. Baker. 2005. Mitochondrial DNA variation in water shrews (Sorex palustris, Sorex bendirii) from western North America: implications for taxonomy and phylogeography. Can. J. Zool. 83:1469-1475.
Pacific Water Shrew Recovery Team. 2007. Recovery strategy for the Pacific Water Shrew (Sorex bendirii) in British Columbia. October Draft. 26pp.
Pacific Water Shrew Recovery Team. 2009. Recovery strategy for the Pacific Water Shrew (Sorex bendirii) in British Columbia. Prepared for the B.C. Ministry of Environment, Victoria, BC. 25pp. + append.
Pattie, D. 1973. SOREX BENDIRII. Mammalian Species, 27:1-2.
van Zyll de Jong, C.G. 1983. Handbook of Canadian mammals. 1. Marsupials and insectivores. National Museum of Natural Sciences, National Museums of Canada, Ottawa, Canada. 210 pp.
Verts, V. J., and L. N. Carraway. 1998. Land mammals of Oregon. University of California Press, Berkeley. 668 pp.
Whitaker, J. O. J., and C. Maser. 1976. Food habits of five western Oregon shrews. Northwest Science 50:102-107.
Zuleta, G.A., and C. Galindo-Leal. 1994. Distribution and abundance of four species of small mammals at risk in a fragmented landscape. B.C. Minist. Environ., Lands and Parks, Wildl. Branch. Working Rep. WR-64. Victoria, British Columbia. 80pp.
 

Please visit the website Conservation Status Ranks for definitions of the data fields used in this summary report.

Suggested Citation:

B.C. Conservation Data Centre. 2011. Species Summary: Sorex bendirii. B.C. Minist. of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Jul 6, 2025).