Marsh shrew
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The marsh shrew (Sorex bendirii), also known as the Pacific water shrew, Bendire's water shrew, Bendire's shrew and Jesus shrew is the largest North American member of the genus Sorex (long-tailed shrews). Primarily covered in dark-brown fur, it is found near aquatic habitats along the Pacific coast from southern British Columbia to northern California. With air trapped in its fur for buoyancy, marsh shrews can run for three to five seconds on top of the water. It measures about Template:Convert in length, including a Template:Convert-long tail, and weighs an average of Template:Convert. The marsh shrew's diet consists mainly of invertebrates, which it hunts on land and in the water. They are rare; their populations are thought to be in decline, and they are considered endangered in parts of their range.
DescriptionEdit
Template:Multiple image The marsh shrew is the largest member of the genus Sorex in North America,Template:Sfn and mammalogist David Nagorsen described it as "an attractive mammal".Template:Sfn Its fur is primarily dark brown, and it has a long tail.Template:Sfn Although the marsh shrew's fur is usually uniformly dark on its back and abdomen,Template:Sfn the abdominal fur of populations (S. b. albiventer) on the Olympic Peninsula may be white.Template:Sfn The marsh shrew is about Template:Convert in length, including a Template:Convert-long tail, and weighs about Template:Convert.Template:Sfn Its hind feet, slightly fringed with coarse hairs on the toes,Template:Sfn measure about Template:Convert.
Although in some areas the marsh shrew is sympatric with other members of the genus Sorex,Template:Sfn no other large, velvety, gray-black shrew shares this geographic range.Template:Sfn Its size distinguishes it from all but the American water shrew (Sorex palustris).Template:Sfn Although the marsh shrew and the American water shrew (the two largest shrews in North America) share some features,Template:Sfn the American water shrew has more dark-grey-to-black fur on its back, a silver-grey belly and a bi-colored tailTemplate:Sfn and the marsh shrew's fringed hairs are more distinct.Template:Sfn The American water shrew has a smaller skull, without the marsh shrew's characteristic curvature, and its upper incisors have less-distinct medial tines.Template:Sfn The marsh shrew typically has a longer snout than that of the American water shrew, which is more streamlined when viewed from the side.Template:Sfn
The marsh shrew's skull is relatively large,Template:Sfn and its condylobasal skull length is usually greater than Template:Convert.Template:Sfn There is a distinctive, downward-sloping curve along the snout (rostrum).Template:Sfn Its dental formula is incisors: 1/1; unicuspids: 5/1; premolars: 1/1; molars: 3/3.Template:Sfn Of the five upper unicuspids the third is distinctly smaller than the fourth, and they have a pigmented ridge extending to the cingulum.Template:Sfn There is a large medial tine on the large upper incisor, in the anterior pigmented region.Template:Sfn The reddish pigmentation of the enamel, the result of iron deposits, is thought to be an adaptation strengthening the enamel.Template:Sfn
There are no known fossil remains.Template:Sfn The marsh shrew's karyotype somatic number is 2n = 54, and its fundamental number = 70.Template:Sfn
Taxonomy and namingEdit
It was first described in the scientific literature in 1884 by Clinton Hart Merriam with its original name, Atophyrax bendirii (a monotypic taxon at the time).Template:Sfn The first specimen was obtained Template:Convert southeast of Fort Klamath in Klamath County, Oregon, at a location Template:Convert from the Williamson River.Template:Sfn Merriam obtained the specimen from Charles Bendire, an ornithologist and army captain stationed at Fort Klamath.Template:Sfn The shrew was caught in late July or early August by one of the dogs in the camp, and a soldier gave it to Bendire. Merriam named it Bendire's shrew (Atophyrax bendirii) in appreciation of Bendire's contribution.Template:Sfn Merriam reported that the animal represented a new genus, Atophyrax, deriving from the Greek and meaning "anomalous sorex".Template:Sfn The marsh shrew was later reclassified in the genus Sorex.
The marsh shrew and the American water shrew (Sorex palustris) share many physical characteristics. The former is found in a narrower area from the northwest coast to the lower slopes of the inland mountains. The American water shrew is more widely distributed across the western mountains and through the subarctic regions of Canada and the eastern U.S.Template:Sfn The species' ranges are primarily allopatric; although they may overlap (sympatry) in coastal regions of the Pacific Northwest, differences in elevation tend to separate them.Template:Sfn Early taxonomists placed these mammals into separate subgenera; Merriam assigned the marsh shrew to Atophyrax, and Jackson (1928) assigned the Pacific water shrew to Neosorex. A closer, dentition-based relationship was assigned by Findley (1955), with both species assigned to the subgenus Otisorex.Template:Sfn Findley hypothesized that in the early Pleistocene, the ancestors of masked and vagrant shrews (Sorex cinereus and Sorex vagrans, respectively) diverged;Template:Sfn during the Yarmouth interglacial, the American water shrew and marsh shrew diverged from their vagrant-shrew ancestors.Template:Sfn Three other Sorex species evolved during the Sangamonian Stage: the dwarf shrew (S. nanus), the southeastern shrew (Sorex longirostris) and the ornate shrew (Sorex ornatus).Template:Sfn Findley's assignment of the marsh shrew and the American water shrew to Otisorex was later reinforced by biochemical and genetic studies. In 2005, findings were published (based on mitochondrial DNA analysis) which better defined the nature of the relationships between marsh shrews, Pacific water shrews and their respective subspecies. Variations in the sequencing of cytochrome b mitochondrial DNA were assessed, and the results of the 2005 phylogeny for the marsh shrew are shown below in detail.Template:Sfn
SubspeciesEdit
The marsh shrew has three subspecies:Template:Sfn
- S. bendirii albiventer (Merriam, 1895)
- S. bendirii bendirii (Merriam, 1884)
- S. bendirii palmeri (Merriam, 1895)
S. b. albiventer is found on the Olympic Peninsula of Washington, S . b . bendirii in the Cascades and southwestern British Columbia and S. b. palmeri in coastal Oregon. These specifications have historically been based on fur markings, skull shape and dental details of unclear significance, and their validity is uncertain.Template:Sfn
Distribution and habitatEdit
The geographic range of the marsh shrew extends from southwest British Columbia, along the western regions of the U.S. states of Washington and Oregon and through northwestern California to the area north of San Francisco.Template:Sfn The subspecies S. b. albiventer is found on the Olympic Peninsula. S. b. palmeri is found from western Oregon (south of the Columbia River) to extrema northwestern California. S. b. bendirii is found from the northern parts of the range (except for the Olympic Peninsula) south along the eastern range to the remaining range in California.Template:Sfn In British Columbia the eastern limits are the Chilliwack River and Agassiz, and the northern limits are the low elevations on the north shore of Burrard Inlet.Template:Sfn
Marsh shrews typically live in wetlands (such as marshes), and their habitat includes extensive forest canopy and ground cover from shrubs, logs, and debris;Template:Sfn they may also be found in riparian environments.Template:Sfn During cold, rainy seasons, they may travel as much as a kilometer from wet areas to more sheltered habitats;Template:Sfn these generally include mixed deciduous or coniferous forest with downed logs and surface cover.Template:Sfn Marsh shrews have been collected from near sea level to as high as Template:Convert in the Cascades.Template:Sfn They may inhabit forests of red alder, bigleaf maple, western hemlock or redcedar, often near marshes with western skunk cabbage.Template:Sfn In British Columbia the marsh shrew is generally found below Template:Convert, but it has been collected at Template:Convert in Mount Seymour Provincial Park.Template:Sfn Environmental officials in British Columbia believe that marsh shrews are one of the rarest small mammals in the province.<ref name=Ministry>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In 1992, Carlos Galindo-Leal and Gustavo Zuleta trapped 1,000 small mammals at 55 locations in a large area of southwestern British Columbia; only three were Pacific water shrews.Template:Sfn
During spring and summer 1983, biologists in western Oregon studied small-mammal distribution (including marsh shrews) near streams and along the riparian fringes of coniferous forests. "Riparian fringe" was defined as at least 15–20 m from a stream. The North American deermouse was caught in greater numbers than any other mammal, representing around 80% of all captures. Sixteen species were trapped, with the marsh shrew representing less than two percent of mammals captured in this study. All the marsh shrews were trapped at streamside, and were found in all three ages of coniferous forests: old-growth, mature and young growth.Template:Sfn
Behavior and ecologyEdit
The marsh shrew eats invertebrates, including spiders, earthworms, sowbugs, centipedes, termites and other terrestrial and aquatic arthropods.Template:Sfn It was observed in captivity pursuing and killing a goldfish, but not eating it.Template:Sfn In contrast, the American water shrew has been observed killing and eating fish.Template:Sfn A study of the gastric contents of marsh shrews in Oregon indicated that at least 25% of their diet is aquatic,Template:Sfn including insect larvae, slugs and snails, mayfly naiads and other, unidentified invertebrates.Template:Sfn Other researchers have reported that their diet may also include aquatic insects (water beetles and stonefly nymphs), craneflies, ground beetles, spiders, harvestmen, centipedes, earthworms, slugs and small terrestrial snails.Template:Sfn The marsh shrew swims, making short dives in search of food;Template:Sfn its mobile snout, whiskers and lips are used to find and capture underwater prey.Template:Sfn Before eating, it returns to land.Template:Sfn Air trapped in its fur provides buoyancy, and marsh shrews can run for as long as 3 to 5 seconds along the top of the water.Template:Sfn According to mammalogist Donald Pattie, they can "scull on the surface like whirligig beetles".Template:Sfn The air trapped in its fur gives it a silvery sheen.Template:Sfn On land, its foreleg and opposite hind leg move at the same time.Template:Sfn
It is active throughout the year, primarily at night. Gestation is about three weeks, and the female has a litter of three or four young.Template:Sfn Nests in the wild, built from shredded bark,Template:Sfn are in a tunnel or under a log. Marsh shrews typically live about 18 months,Template:Sfn and males are not thought to reach sexual maturity during their first summer.Template:SfnTemplate:Sfn Since their lifespan is short, they apparently breed for only one season.Template:Sfn Although no breeding data exist for British Columbia, the breeding season elsewhere is from late January to late August; most young are born in March.Template:Sfn The number of litters a female rears is unknown.Template:Sfn
The strong odor associated with marsh shrews (in common with other long-tailed shrews) may be a means of communication.Template:Sfn Similar to other shrews, they have poor eyesight.Template:Sfn If a marsh shrew is placed in a foreign environment (such as along an edge of a raised surface), it will run off the edge and continue to run after landing on the surface below.Template:Sfn Landing in water, it dives beneath the surface.Template:Sfn Marsh shrews are easily trapped in sunken cans, possibly due to their inability to see where the edges of surfaces drop.Template:Sfn In captivity they vocalize when they are displaced or scuffle with other animals in their cage,Template:Sfn twittering shrilly if disturbed while eating or in a confrontation over food (such as a worm).Template:Sfn Although it is uncertain whether marsh shrews cache (or hoard) food in the wild,Template:Sfn in captivity they set aside nightcrawlers in a corner of the cage for later consumption;Template:Sfn no other food items were set aside in this fashion.Template:Sfn
Acarine parasites include the Glycyphagidae (Glycyphagus hypudaei and Orycteroxenus soricis); the Laelapidae (Androlaelaps fahrenholzi, Echinonyssus obsoletus, Haemogamasus occidentalis and Haemogamasus reidi); the Listrophoridae (Listrophorus mexicanus); the Myobiidae (Amorphacarus hengererorum, Amorphacarus soricis, Protomyobia atophyracis and Protomyobia brevisetosa), and the Pygmephoridae (Pygmephorus horridus and Pygmephorus whitakeri).Template:Sfn Probable predators include owls, fish and the Pacific giant salamander.Template:Sfn
Template:AnchorHuman interactionEdit
Before Donald Pattie's research during the late 1960s, when his team studied marsh shrews in captivity, little was known about their behavior.Template:Sfn Before then, most information about the marsh shrew was from notes about the mammal's habitat and information about trapping it. Its descriptions in the literature were largely derived from the examination of museum specimens.Template:Sfn
Conservation statusEdit
Marsh shrews are listed as "Endangered" by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC),Template:Sfn their habitat in British Columbia limited to the lower Fraser Valley. Their available habitat continues to degrade as a result of economic activity in the area; with little chance of the trend reversing, they are rare in that part of Canada. COSEWIC designated the marsh shrew as "Threatened" from April 1994 until May 2000, updating its status in April 2006 to "Endangered."<ref name=NatureServe>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> According to the IUCN, marsh shrews are of "Least Concern" in terms of conservation. Although the shrew is considered a rare mammal and its numbers are thought to be in decline, no population estimates are currently provided and its rate of decline is not considered fast enough to warrant placing it in a more-threatened category. Suitable wetland habitat is declining, due primarily to urbanization and the conversion of habitat to agriculture, and areas of protected habitat are expected to be provided in the shrew's broad geographic range.Template:Sfn
ReferencesEdit
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Further readingEdit
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External linksEdit
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