Sorex navigator
| Western Water Shrew
(Sorex navigator) | |
|---|---|
| Range | |
 | |
| Taxonomic classification | |
| Order: | Eulipotyphla |
| Suborder: | Erinaceota |
| Superfamily: | Soricoidea |
| Family: | Soricidae |
| Subfamily: | Soricinae |
| Tribe: | Soricini |
| Genus: | Sorex |
| Subgenus: | Otisorex |
| Species group: | Sorex palustris group |
| Binomial details | |
| Sorex navigator (S. F. Baird, 1857) | |
| Other resources | |
| Full taxonomic details at MDD | |
Split from Sorex palustris by Hope et al. (2014), Sorex navigator includes S. navigator alaskanus.
From Woodman (2018): "Hope et al.’s (2014) investigation of the molecular phylogenetics of North American water shrews revealed three species-level clades among the subspecies formerly united as Sorex palustris: eastern Sorex albibarbis, western cordilleran Sorex navigator, and boreal Sorex palustris (sensu stricto). Nagorsen et al. (2017) demonstrated that parapatric S. navigator and S. palustris can be distinguished morphometrically."
Description
From Armstrong et al. (2010), describing S. palustris, which is now S. navigator: "The water shrew is a beautiful, distinctive mammal, a large dark shrew with a long tail. The tail is distinctly bicolored and about the same length as the body. There is a conspicuous fringe of stiff hairs along the toes and margin of the relatively large hindfeet. The sexes are similar in size and coloration, although mature males generally weigh more than females. There are two molts per year, but little difference in color of texture between them."
From Verts & Carraway (1998): "Sorex navigator is a very large shrew with dark gray to black dorsal pelage, a white venter and throat, and a sharply bicolored tail." The summer coloration is slightly brownish. The hind foot is fimbriated (is bordered by a stiff fringe of hairs).
Museum type specimens
The images shown below are of the holotype for Sorex navigator alaskanus because the skin of Holotype:USNM 629 Sorex navigator is heavily damaged.
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Holotype: USNM 97713. Sorex navigator alaskanus. Adult male. Point Gustavus, Glacier Bay, Alaska. Collected 12 June 1899. -
Holotype: USNM 97713. Sorex navigator alaskanus. Adult male. Point Gustavus, Glacier Bay, Alaska. Collected 12 June 1899.
External measurements
Length measurements are in millimeters (mm) and weight measurements are in grams (g), unless stated otherwise. If available, the sample size (n=) is provided. If a range is not provided and n= is not given, then the listed measurement represents an average.
| Part of range | Reference | Total length | Tail length | Hindfoot length | Ear length | Mass |
|---|---|---|---|---|---|---|
| California | Jameson & Peeters (2004) | 144–158 | 73–78 | 18–21 | 6 | 8–14 |
| Oregon | Verts & Carraway (1998) | 130–170 | 65–79 | 18–22 | 6.5–17.2 |
Skull
| Sorex navigator skull characters | |
|---|---|
| units in mm | |
| Skull | |
| Condylobasal length: | 19.1–21.7 (Beneski & Stinson, 1987); up to 22 (Armstrong, 2010) |
| Postmandibular canal: | Absent |
| Dental | |
| Upper unicuspids: | 5 |
| Unicuspid notes: | U3<U4; U2>U1 |
| Tines present: | Yes; although lacking in some individuals |
| Tine size: | Tiny |
| Tine position: | Well below upper limit of pigment on upper incisors |
| Shape upper incisors: | Diverging |
Diagnosis from Jameson & Peeters (2004): "Inner side of lower jaw without postmandibular canal; inner (median) surface of unicuspid teeth with pigmented ridge; third upper unicuspid smaller than fourth; skull length greater than 19.0 mm; first unicuspid smaller than second; hindfoot with distinct lateral fringe of stiff hairs."
From Armstrong et al. (2010), describing S. palustris, which is now S. navigator: "The skull is stout and long for a shrew of the genus Sorex, with greatest length up to 22 mm. There are 5 unicuspid teeth in each side of the upper jaw, with the fifth much smaller than the others but still visible in a lateral view. The third unicuspid is smaller than the fourth."
Many of the images shown below are of the holotype for Sorex navigator alaskanus because the skull of Holotype:USNM 629 Sorex navigator is damaged.
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Holotype: USNM 97713. Sorex navigator alaskanus. Adult male. Point Gustavus, Glacier Bay, Alaska. Collected 12 June 1899. -
Holotype: USNM 97713. Sorex navigator alaskanus. Adult male. Point Gustavus, Glacier Bay, Alaska. Collected 12 June 1899. -
Holotype: USNM 97713. Sorex navigator alaskanus. Adult male. Point Gustavus, Glacier Bay, Alaska. Collected 12 June 1899. -
Holotype: USNM 629/1780. Sorex navigator. Age and sex not given. Near head of Yakima River, Cascade Mountains, Kittitas County, Washington. Collected 31 August 1853. -
Holotype: USNM 97713. Sorex navigator alaskanus. Adult male. Point Gustavus, Glacier Bay, Alaska. Collected 12 June 1899. -
Holotype: USNM 97713. Sorex navigator alaskanus. Adult male. Point Gustavus, Glacier Bay, Alaska. Collected 12 June 1899. -
MVZ:Mamm:224386. Sorex navigator. Dorsal view of the skull. -
Upper incisors of Sorex navigator, scale is 0.5 mm. Borrowed from Nagorsen et al. (2017). -
MVZ:Mamm:224386. Sorex navigator. Unicuspids, scale is 1 mm.
Taxonomic notes
From Woodman (2018): "Hope et al.’s (2014) investigation of the molecular phylogenetics of North American water shrews revealed three species-level clades among the subspecies formerly united as Sorex palustris: eastern Sorex albibarbis, western cordilleran Sorex navigator, and boreal Sorex palustris (sensu stricto). Nagorsen et al. (2017) demonstrated that parapatric S. navigator and S. palustris can be distinguished morphometrically."
Similar species
In the USA, the only species that Sorex navigator it might be confused with is the Marsh Shrew (Sorex bendirii) and the American Water Shrew (Sorex palustris) from which it was split.
Comparison with Sorex bendirii
Sorex navigator is a large gray to black shrew with a white venter and throat and hind feet that are bordered by a noticeable fringe of stiff hairs (Pattie, 1973). The Marsh Shrew (Sorex bendirii) is also large, but uniformly dark (except for the Olympic peninsula where the venter may be whitish—Pattie, 1973). In S. bendirii there is a slight fringe of stiff hairs on the hind toes (Pattie, 1973). When comparing skulls, the tines on the medial edges of the upper incisors are more robust in S. bendirii than in S. navigator.
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Ranges of the Marsh Shrew (Sorex bendirii) and the Western Water Shrew (Sorex navigator). -
Upper incisors of the Marsh Shrew (Sorex bendirii). -
Upper incisors of the Western Water Shrew (Sorex navigator). Borrowed from Nagorsen et al. (2017). -
Unicuspids of the Marsh Shrew (Sorex bendirii), scale is 1 mm. Note that this is the skull of an older individual and the teeth are worn. -
Unicuspids of the Western Water Shrew (Sorex navigator), scale is 1 mm.
Comparison with Sorex palustris
Sorex navigator was split from S. palustris in 2014 by Hope et al. Nagorsen et al. (2017) provides the following information for distinguishing S. navigator from S. palustris: "We found no differences in external morphology. Both species had five paired pads on digits 3 and 4. Dorsal and ventral pelage colour and the degree of bicolouring of the tail varied among individuals, but we observed no interspecific differences. Similarly, the bristle fringe of hairs on the hind feet and degree of lateral flattening of the tail was similar in both species. In both species, ventral pelage colour ranged from silvery-grey to brown. Sorex navigator from Vancouver Island differed from other samples in having brown markings on the ventrum. Dorsal pelage colour of S. navigator and S. palustris ranged from brown to black with some individuals of each species showing white tips on dorsal guard hairs. Both taxa had distinctly bicoloured tails with a paler underside... Pigmentation on the anterior face of I1 [upper incisor] and its associated tine was generally darker extending higher on the tooth in S. navigator compared with S. palustris."
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Range of the Western Water Shrew (Sorex navigator). -
Range of the American Water Shrew (Sorex palustris). -
Upper incisors of the Western Water Shrew (Sorex navigator). Borrowed from Nagorsen et al. (2017). -
Upper incisors of the American Water Shrew (Sorex palustris). Borrowed from Nagorsen et al. (2017).
References
Armstrong DM, Fitzgerald JP, Meaney CA. 2010. Mammals of Colorado, Second Edition. Denver (CO, USA): University Press of Colorado.
Baird SF. 1857. Mammals. In Reports of Explorations and Surveys to Ascertain the Most Practicable and Economical Route for a Railroad from the Mississippi River to the Pacific Ocean. Part 1. General Report upon the Zoology of the Several Pacific Railroad Routes, Volume 8, bk. 1. Washington, D.C.
Beneski JT, Stinson DW. 1987. Sorex palustris. Mammalian Species (296): 1-6.
Hope AG, Panter N, Cook JA, Talbot SL, Nagorsen DW. 2014. Multilocus phylogeography and systematic revision of North American water shrews (genus: Sorex). Journal of Mammalogy 95(4): 722-738.
Jameson EW, Peeters HJ. 2004. Mammals of California (No. 66). Berkeley (CA, USA): University of California Press.
Nagorsen DW, Panter N, Hope AG. 2017. Are the western water shrew (Sorex navigator) and American water shrew (Sorex palustris) morphologically distinct?. Canadian Journal of Zoology 95(10): 727-736.
Verts BJ, Carraway LN. 1998. Land mammals of Oregon. Berkeley (CA, USA): University of California Press.
Woodman N. 2018. American Recent Eulipotyphla: Nesophontids, Solenodons, Moles, and Shrews in the New World. Smithsonian Contributions to Zoology. https://doi.org/10.5479/si.1943-6696.650