Pacific Water Shrew
Limited range, natural rarity, and accelerating development of habitat for human use combine to place these mammals in great peril.
Province of British Columbia Ministry of Environment, Lands and Parks large tracts of forest. Little suitable habi- 55 sites in a variety of forest types pro- tat occurs within protected areas. duced 999 individuals of 15 species of Even more troubling are trends that small mammals, some rare and some suggest that this habitat loss will con- abundant. Only three Pacific Water Why are Pacific Water tinue, and even accelerate. In Greater Shrews were found (0.3 percent of the Shrews at risk? Vancouver, the human population has total); one in each of three widely scat- acific Water Shrews, also known doubled in the past 30 years and is pro- tered locations, in Coquitlam, White as Marsh Shrews, are threatened jected to exceed 2 million by 2011. This Rock, and near Stave Lake. In 1995, Pa- in British Columbia by habitat population growth has been accompa- cific Water Shrews were found at two Pdestruction within their very nied by a 24 other locations where they had been his- restricteddistribution range. The natural percent reduc- torically reported, near Sumas Moun- These relatively large shrews occur range of tion in natural tain and Abbotsford. along the Pacific Coast from vegetation in the Few Pacific Water Shrews from Brit- northern California to southern Pacific Water past 16 years. In ish Columbia occur in museum collec- British Columbia, where they are Shrews the Township of tions. Of these, over 80 percent were found only in the lower Fraser Langley, for ex- obtained before 1950. Most of these Valley. Within that range, about unfortunately ample, 70 per- were collected before 1900 at Sumas, 0.5 percent of the area of the prov- coincides with cent of land is near Chilliwack, a location where little ince, they are one of the rarest now unsuitable suitable habitat is now present. These small mammals and have prob- the major for forest-dwell- records, together with more recent sur- ably always been uncommon. urban area in ing small mam- veys, suggest that Pacific Water Shrews Limited distribution range, natu- mals. These trends have declined in abundance in British ral rarity within that range, and British are evident across Columbia over the past century. The accelerating development of Columbia – much of the best lowland habitats have probably wildland habitats for human use Fraser Lowland been destroyed and the remaining Pa- combine to place these mammals the Lower and suggest a cific Water Shrew populations are con- in great peril. Mainland. bleak future in- fined to marginal habitats around the The natural range of Pacific deed for the fringes of the Fraser Valley. Water Shrews unfortunately coin- Pacific Water Recognizing this perilous status, BC cides with the major urban area in Brit- Shrew and other wildlife species having Environment assigned the Pacific Water ish Columbia – the Lower Mainland. a similar distribution. Shrew to its Red List in 1993. Red-listed Much of their preferred habitat – valley wildlife species are candidates for legal bottom forestland along streams and What is their status? designation as Endangered or Threat- wetlands – has been converted to farm- he total number of Pacific Water ened under the British Columbia Wild- land, subdivisions and industrial sites. Shrews living in British Columbia is life Act. Even without such designation, Ditching and drainage schemes and not known, and would be almost however, the Pacific Water Shrew, like stream pollution have had harmful ef- T impossible to determine. These most wildlife in the province, is fects on many riparian habitats. Around shrews are known to be quite rare protected from the fringes of the settled lands, logging throughout their range, even at The Pacific killing or collect- has removed much forest cover and the centre of their distribution in Water Shrew ing by provisions streamside strips left to protect fisheries Washington and Oregon. Field of the Wildlife values are mostly too narrow to benefit surveys in several areas have was designated Act. In a nation- these shrews. Many sites where Pacific shown Pacific Water Shrews to al- as Threatened al context, the Water Shrews once occurred have now ways make up under 1 percent of Pacific Water been lost. Of 24 Lower Mainland sites all small mammals (mice and in Canada Shrew was given where the species has been recorded shrews) detected. In 1992, BC En- in . Threatened sta- since 1894, 11 are now in isolated vironment sponsored extensive tus by the Com- patches within urban areas, 8 are in rap- surveys in the Lower Mainland to mittee on the idly developing lands between urban try to locate Pacific Water Shrews and Status of Endangered Wildlife in and forested zones, and only 5 are inside other rare small mammals. Sampling at Canada () in 1994. This was in- and immediately adjacent areas is prob- ably a Pacific Water Shrew. Because so little is known about Pacific Water Shrews in this area, anyone making a positive sighting or finding a dead specimen should report it to the Minis- try of Environment, Lands and Parks office in Surrey.
What makes them unique? hrews are ancient mammals, and have evolved their distinctive char- acteristics over several million years. S Pacific Water Shrews probably be- came differentiated from their close relatives the Water Shrews during the ice age when these shrews were isolated south of the ice sheet, the Pacific Water Shrew along the Pacific Coast of California and Oregon, the Water Shrew further east. As the glaciers based on its rarity and restricted range prominent whiskers on the snout, and melted back, the Pacific Water Shrew, in Canada, its dependence on special side glands that produce a musky and other mammals like the Coast riparian habitats, and the rate of habitat odour. and Townsend’s Moles, Shrew-Mole, loss within its range. Of nine kinds or species of shrews in Creeping Vole and Townsend’s Vole, the province, five may occur within the moved northward into the Puget What do they look like? range of the Pacific Water Shrew in the Sound and Fraser Lowlands. As a result, hrews are diminutive, hyperactive Lower Mainland. Four of these species, the northern edge of the Fraser Low- mammals, most species being the Common, Dusky, Vagrant and land is one of the most distinctive smaller than an average mouse. Trowbridge’s Shrews, are all zoogeographic S Shrews differ from mice in having a smaller than the Pacific Water A Pacific boundaries in long pointed snout, short velvet-like Shrew, and usually average 10 to Water Shrew North America. fur, tiny eyes, and sharp teeth that are 12 cm in total length, including The Pacific Water designed for shearing their insect prey. the tail. The fifth species is the can run on Shrew is an im- Their relatives, the moles, also have closely related Water Shrew, a top of the portant compo- pointed snouts and velvety fur, but un- similar-sized species found across nent of this unique like shrews have broad paddle-like feet Canada and in the northern water for faunal assemblage, for digging, and no external ears. United States. The Water Shrew is periods of and further stud- The Pacific Water Shrew (Sorex found in mountains north of ies of it could bendirii) is the largest shrew in British Burrard Inlet and the Fraser Val- several aid in unravelling Columbia, averaging 15 cm in total ley and could be confused with the seconds. the mysteries of length, of which the tail makes up nearly Pacific Water Shrew if not exam- post-glacial evolu- half. The fur is blackish brown to black ined closely. However, the Water tion and land- in colour. The belly may be a slightly Shrew has white or grey underparts, and scape change in southwestern British lighter, dark-grey hue. The tail is also the underside of its tail is also white. In Columbia. dark. Its feet are brownish and fringed the small area where their ranges over- Pacific Water Shrews are unique with short stiff hairs that aid in swim- lap, the Water Shrew usually lives at among lower Fraser Valley shrews in ming. Like other shrews, this species has higher elevations. Any dark-bodied terms of their large size, habitat selec- short legs, five clawed toes on each foot, shrew over 14 cm long encountered be- tion, and food habits. More than any short ears that are partly hidden by fur, low 500 m elevation in the Fraser Valley other shrew within their range, Pacific Water Shrews are specialized for an mentary, unopened ears. The growth of Present range of the Pacific aquatic mode of life. They are seldom young is believed to be rapid but the Water Shrew in Canada found more than 50 m from sluggish length of time spent in the nest remains and the United States streams and wetlands, and swim and unknown. After they leave the nest, ju- dive readily in search of underwater venile Pacific Water Shrews tend to dis- prey. They also have the most special- perse. Males have side glands that pro- ized food habits, feeding on a narrower duce a strong musky odour believed to range of food items, a higher proportion be important in finding mates. of insects, and more foods of aquatic origin than is the case for other shrews What do they eat? in the same area. arval stages of freshwater insects, in- cluding mayflies, stoneflies and How do they reproduce? other species, are among the most ery little is known about the repro- L important foods of Pacific Water ductive life of the Pacific Water Shrews. Other favoured prey are snails, Shrew. Shrews in general live less slugs, earthworms, and spiders. This Vthan 18 months and this probably shrew obtains much of its food from the also applies to Pacific Water Shrews. Pa- streams and ponds along which it lives, cific Water Shrews are not believed to and is remarkably adapted for this reach sexual maturity in their first sum- aquatic existence. A Pacific Water mer, so they have only one spring-sum- Shrew can actually run on top of the mer breeding season in their lifetime. water for periods of three to five sec- This short lifetime is to some extent onds, with its belly above or just touch- compensated for by production of two ing the water! More frequently it swims two minutes, but may be longer if prey or three litters of three to six young. The frantically on the water surface, sculling items are found. While underwater, the gestation period of related shrews, and whirling like a giant beetle, then shrew uses its flexible snout and sensi- about 18 to 21 days, is probably similar submerges to hunt. Underwater pro- tive whiskers to probe crevices in search in Pacific Water Shrews. Young Pacific pulsion is by alternating strokes of the of food; normal swimming activity Water Shrews are born and nursed in a large, fringed hind feet. nest, typically made of shredded bark Bubbles trapped in the and hidden under the loose bark of a fur give a silvery appear- fallen tree or similar hiding place. When ance when the shrew is born the young are poorly developed submerged, and aid in and hairless. Newborn young huddle insulation against the together in a ball to preserve body heat. cold water. Bouts of Their eyes are visible as black spots swimming in search of through red skin and they have rudi- food are usually under
Hope
Nanaimo Distribution of the Pacific Water Shrew in British Columbia
Historic range ’ Recent records Victoria , , . creases frantically when prey animals and other wetlands. Although occasion- Pacific Water Shrews are usually are detected. In captivity, Pacific Water ally found up to 350 m from streams, found in relatively extensive tracts of Shrews make frequent trips to the water detailed studies in Washington and Or- forest. Many forest fragments isolated in each day for foraging, and probably do egon have found most to be within 50 m settled areas of the Fraser Valley are too so in the wild as well. of water. Being adapted to a semi- small to support shrew populations, al- Captured food is taken out of the aquatic existence and heavily dependent though the minimum size needed for water before it is devoured. Only the their survival isn’t known. Pacific Water soft parts of hard-bodied prey like snails Shrews are expected to have long nar- and beetles are eaten. Large earthworms row home ranges parallel to streams, are subdued by lightning-like bites therefore lengthy tracks of riparian along their length before being con- habitat are probably needed to support sumed. a population. Shrews are among the smallest warm-blooded animals, and therefore What can we do? have a high rate of heat loss in propor- C Environment is focusing more tion to body size. They compensate with attention on the plight of the Pacific a high metabolic rate, which also means Water Shrew by assigning it to the they must consume a lot of food. It has Bprovincial Red List, distributing been estimated that mammals the size status information, and sponsoring of the Pacific Water Shrew need to eat at field surveys. The B.C. Conservation least their own body weight in food each Data Centre maintains a database, avail- day if they are to survive. How these able to researchers and the public, on non-hibernators manage to do this in this and other rare species. winter remains a mystery. At any rate, A major and pressing need is for food-finding is the major life-long, day preservation of remaining habitats and night preoccupation of these hy- occupied by Pacific Water Shrews. Un- . Bruce Runciman photo peractive little mammals. fortunately, the species is so rare in Brit- on freshwater organisms for food, Pa- ish Columbia that reliable information Where do they live? cific Water Shrews need riparian habi- on its regional abundance and most acific Water Shrews are found only tats to survive. This shrew is more important habitats will take much from northern California to ex- strongly associated with riparian situa- time and effort to collect. Greater atten- treme southern British Columbia, tions than any other shrew or mouse tion must be given to preserving Pwest of the summit of the Cascade within its range. Pacific Water riparian Range. This area is characterized by Shrews are generally more abun- Support forestland moist, temperate coniferous forest, its dant in mature and old-growth stewardship within the lower elevations being dominated by forests than in younger stands, range of the Douglas-fir. In British Columbia, Pa- and are seldom found in clearcuts initiatives and Pacific Wa- cific Water Shrews have been recorded or farmlands. Their forest habitats the establishment ter Shrew. south of the Fraser River from White may be dominated by coniferous The riparian Rock to Cultus Lake and Chilliwack, trees like Douglas-fir or mixed of parks and zone is a key and north of the river from Point Grey stands of conifers, red alder, and reserves along habitat type and North Vancouver to the vicinity other deciduous trees and shrubs. for many of Stave Lake and Agassiz. They have They seem to prefer sites where streams and mammals, been found up to the 1300 m elevation the forest floor has abundant around wetlands. birds, am- in the southern part of their range, fallen and rotting logs, as well as a phibians and but not above the 850 m level in British good cover of fine litter. Charac- reptiles, Columbia. teristics of the understorey and forest some of which are as rare as the Throughout their range, Pacific Wa- floor may be as important, or more im- Pacific Water Shrew. This is particularly ter Shrews are usually found near slug- portant, than the kind and density of the important on suburban and forest- gish low-elevation streams, marshes forest canopy. fringe lands where development for . . David Nagorsen photo Paul vanPeenen photo housing, agriculture or other uses is target the Pacific Water Shrew. Shrews by supporting stewardship ini- imminent. Members of the public are urged to tiatives and the establishment of parks Lands devoted to forestry, whether become more familiar with this poorly and reserves along streams and around Crown or private, also need attention. known shrew. Sightings, specimens, or wetlands in the Fraser Valley area. Habi- Streamside strips of mature or old- observations of activities threatening its tat protection is urgently needed. With growth forest should be permanently habitat should be reported to the near- your help, this remarkable mammal and maintained, and need to be wide est BC Environment office. People can other rare species found with it will enough to support shrew populations. also aid the survival of Pacific Water continue to enrich our fauna. Narrow leave strips that have tradition- ally been saved to protect fishery re- sources are not wide enough for most riparian wildlife. Hopefully, 30 to 50 m wide riparian management areas along streams and around wetlands and lakes, as now prescribed by the Forest Prac- tices Code, will be an improvement. However, some researchers have suggested that buffer strips of 60 to , : 100 m may be needed for Pacific Wildlife Branch Water Shrews. BC Environment Additional attention should also Ministry of Environment, Lands and Parks be given to restoring the quality of ur- 780 Blanshard Street ban and rural streams that have Victoria, British Columbia V8V 1X4 been damaged by pollution, erosion, channelization, and other activities. In some cases it may be possible to re- connect short segments of riparian woodland partitioned by human land uses in past years. Further field surveys of this intrigu- ing mammal are needed to identify critical habitats. These surveys should --- . be directed at promising habitats . that have not been surveyed before, , and use techniques that specifically Printed in British Columbia on recycled paper with vegetable base inks. ..