Sorex arcticus
Arctic Shrew
(Sorex arcticus) | |
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Range | |
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Taxonomic classification | |
Order: | Eulipotyphla |
Suborder: | Erinaceota |
Family: | Soricidae |
Subfamily: | Soricinae |
Tribe: | Soricini |
Genus: | Sorex |
Subgenus: | Sorex (subgenus) |
Species group: | Sorex araneus group |
Binomial details | |
Sorex arcticus Kerr, 1792 |
Description
From Kirkland & Schmidt (1996): "The arctic shrew is a medium sized shrew. Adults possess a distinctive tri-colored pelage (Clough, 1963). The dorsum is very dark brown to black, sides are lighter brown, and underparts are grayish-brown. The tail is indistinctly bicolored, brown to brownish-black above and lighter below (van Zyll de Jong, 1983)." Additionally, "In S. arcticus, the light sides contrast strongly with the dark dorsum, especially in winter pelage. Young of the year in summer pelage are lighter in color and bicolored (Junge and Hoffmann, 1981)."
From Naughton (2012): "Adults are dark chocolate brown to blackish in colour on their backs; their sides are lighter brown, sometimes with a rusty tinge around the shoulders and neck; and their bellies are an even paler grey brown to whittish colour. The demarcation between each colour is sharply distinct. The tail is faintly bicoloured, darker above and paler below, and the upper parts of the feet are a dirty buffy brown. Juveniles are generally browner than adults and not as distinctly tricoloured."


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 |
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Canada | Naughton (2012) | 97–125 | 36–48 | 11–19 | 4–9 | 5.1–13.0 |
Great Lakes Region | Kurta (2017) | 105–125 | 37–46 | 12–15 | 7–13 | |
Minnesota | Hazard (1982) | 106–112 | 36–45 | 12–15 | 7.4–10 | 7.1–11.7 |
North Dakota | Seabloom et al. (2020) | 109 | 40 | 14 | 8 | 9.1 |
not reported | Whitaker Jr. & Hamilton Jr. (1998) | 100–124 | 30–45 | 12–15 | 6.0–13.5 | |
rangewide | Wilson & Ruff (editors, 1999) | 100–124 | 36–45 | 5–13.5 | ||
Wisconsin | Kirkland Jr. & Schmidt (1996) | males: 100–121 (n=31); females: 105–124 (n=22) | males: 37–45 (n=31); females: 36–45 (n=22) | males: 12–15 (n=30); females:13–15 (n=23) | males: 6.0–12.3 (n=30); females: 5.3–13.5 (n=24) |
Color variation
This section shows some of the color variation present in Sorex arcticus. The location is provided for reference only. The individual shown does not necessarily represent the only color variant within the local population. From Kirkland and Schmidt (1996): "The tricolored pelage of adults distinguishes this shrew from other sympatric North American soricids. In S. arcticus, the light sides contrast strongly with the dark dorsum, especially in winter pelage. Young of the year in summer pelage are lighter in color and bicolored (Junge and Hoffmann, 1981)."
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North Dakota, Stutsman County, subadult
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Wisconsin, Lincoln County, subadult
Skull
Sorex arcticus skull characters | |
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units in mm | |
Skull | |
Condylobasal length: | 19.1–20.0 (Kirkland & Schmidt, 1996) |
Postmandibular canal: | Present |
Shape: | Skull relatively flat; braincase slightly rounded |
Dental | |
Upper unicuspids: | 5 |
Unicuspid notes: | U3≥U4 |
Tines present: | Yes |
Tine size: | Small |
Tine position: | Well below upper limit of pigment on upper incisors |
Shape upper incisors: | Straight |
Dental characters: | Unicuspids robust and appear bulbous in ventral view; tips of upper incisors are more widely separated partly because of tines |
From Naughton (2012): "There are five readily apparent upper unicuspids, and the third is larger than the fourth."
The lower jaw contains a postmandibular canal. Tines are somewhat small and positioned well below the upper limit of pigment on the upper incisors.
Similar species
Within its range in the United States, Sorex arcticus may be confused with other brown shrews: Masked Shrew (Sorex cinereus), Western Pygmy Shrew (Sorex eximius), Prairie Shrew (Sorex haydeni), and Eastern Pygmy Shrew (Sorex hoyi). In size, S. arcticus is larger than S. cinereus, S. haydeni, and much larger than S. hoyi and S. eximius. It is not likely to be confused with the American Water Shrew (Sorex palustris) as that species is generally much larger than S. arcticus, but size may overlap.
Comparison with Sorex cinereus
In size, Sorex arcticus is larger than the Masked Shrew (Sorex cinereus) and adults have a tricolored pelage. From Kirkland and Schmidt (1996): "In S. arcticus, the light sides contrast strongly with the dark dorsum, especially in winter." Sorex cinereus may have lighter sides, but is smaller in size. When comparing skulls, Sorex arcticus has a lower jaw that contains a postmandibular canal, while the lower jaw of S. cinereus lacks a postmandibular canal. If only the top of the skull is found, S. arcticus can be distinguished from S. cinereus by the length of the skull.
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Sorex arcticus -
Masked Shrew (Sorex cinereus) -
Upper incisors of Sorex arcticus. -
Upper incisors of Masked Shrew (Sorex cinereus). -
Unicuspids of Sorex arcticus. The third unicuspid is slightly larger than the fourth. -
Unicupids of Masked Shrew (Sorex cinereus). Third unicuspid is equal to or slightly larger than the fourth.
Comparison with Sorex eximius and S. hoyi
In size, Sorex arcticus is larger than the Eastern Pygmy Shrew (Sorex hoyi) and the Western Pygmy Shrew (Sorex eximius). Sorex hoyi and S. eximius lack the tricolored pelage of S. arcticus adults. Within its range in the United States, Sorex arcticus is the only species that has a lower jaw that contains a postmandibular canal. The tines on the upper incisors of S. eximius and S. hoyi are far more robust than those of S. arcticus and the skulls are also smaller. The third and fifth upper unicuspids of S. eximius and S. hoyi are also minute.
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Sorex arcticus -
Eastern Pygmy Shrew (Sorex hoyi) -
Western Pygmy Shrew (Sorex eximius) -
Upper incisors of Sorex arcticus. -
Upper incisors of Western Pygmy Shrew (Sorex eximius). -
Upper incisors of Eastern Pygmy Shrew (Sorex hoyi). -
Unicuspids of Sorex arcticus. The third unicuspid is slightly larger than the fourth. -
Unicuspids of Western Pygmy Shrew (Sorex eximius). The third and fifth unicuspids of Sorex eximius and S. hoyi are tiny and vestigial. -
Upper unicuspids of Sorex hoyi. In this individual, the third unicuspid (U3) is tiny and not visible in side view. The fifth unicuspid (U5) is also tiny and just barely visible. Note that this is an old individual and the teeth are worn. In some individuals, the third unicuspid may be barely visible in side view, while the fifth is not.
Comparison with Sorex haydeni
In size, Sorex arcticus is larger than the Prairie Shrew (Sorex haydeni) and adults have a tricolored pelage. When comparing skulls, Sorex arcticus has a lower jaw that contains a postmandibular canal, while the lower jaw of S. haydeni lacks a postmandibular canal. If only the top of the skull is found, it can be distinguished from S. haydeni by the length of the skull.
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Sorex arcticus -
Prairie Shrew (Sorex haydeni)
Comparison with Sorex palustris
It is not likely to be confused with the American Water Shrew (Sorex palustris) as that species is generally much larger than S. arcticus but size may overlap; however, the fur of S. palustris is black or gray frosted with black and it has distinct fringes of stiff hairs on the sides of the feet and toes.The skull of the American Water Shrew (Sorex palustris) is much larger than that of S. arcticus and the tine on the upper incisor of S. palustris is small and located at the upper limit of pigment on the upper incisors. When comparing skulls, Sorex arcticushas a lower jaw that contains a postmandibular canal, while the lower jaw of S. palustris lacks a postmandibular canal.
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Upper incisors of Sorex arcticus. -
Upper incisors of American Water Shrew (Sorex palustris). Borrowed from Nagorsen et al. (2017).
References
Clough GC. 1963. Biology of the arctic shrew, Sorex arcticus. The American Midland Naturalist 69:69-81.
Hall ER. 1981. The mammals of North America. Second edition. John Wiley & Sons, New York.
Hazard EB. 1982. The mammals of Minnesota. Minneapolis (MN, USA): University of Minnesota Press.
Junge JA, Hoffman RS. 1981. An annotated key to the long-tailed shrews (Genus Sorex) of the United States and Canada with notes on middle American Sorex. Occasional Papers of the Museum of Natural History, The University of Kansas, Lawrence Kansas. Number 94; Pages 1-48.
Kerr R. 1792. The Animal Kingdom, or Zoological System of the celebrated Sir Charles Linnaeus. Class I. Mammalia. A. Strahan, T. Cadell, and W. Creech, Edinburgh, 462 pp.
Kirkland GL, Schmidt DF. 1996. Sorex arcticus. Mammalian Species (524): 1-5.
Kurta A. 2017. Mammals of the Great Lakes region. Ann Arbor (MI, USA): University of Michigan Press.
Naughton D. 2012. The natural history of Canadian mammals. Toronto (ON, CA): University of Toronto Press.
Perry ND, Stewart DT, Madden EM, Maier TJ. 2004. New records for the Arctic shrew, Sorex arcticus and the newly recognized Maritime shrew, Sorex maritimensis. The Canadian Field-Naturalist 118(3): 400-404.
Seabloom R, Hoganson JW, Jensen WF. 2020. The mammals of North Dakota. Fargo (ND, USA): North Dakota State University Press.
van Zyll de Jong CG. 1983. Handbook of Canadian mammals. I. marsupials and insectivores. National Museums of Canada, Ottawa, 210 pp.
Whitaker JO, Hamilton WJ. 1998. Mammals of the eastern United States. Ithaca, (NY, USA): Cornell University Press.
Wilson DE, Ruff S, editors. 1999. The Smithsonian Book of North American Mammals. Washington D.C. (USA): Smithsonian Institution Scholarly Press.