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Microtus richardsoni

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North American Water Vole
(Microtus richardsoni)
Range
Taxonomic classification
Order:Rodentia
Suborder:Supramyomorpha
Infraorder:Myomorphi
Superfamily:Muroidea
Family:Cricetidae
Subfamily:Arvicolinae
Tribe:Microtini
Genus:Microtus
Subgenus:Pitymys
Binomial details
Microtus richardsoni (DeKay, 1842)

Microtus richardsoni is the largest vole in North America.

Description

From Ludwig (1984): "The pelage is long with the upperparts grayish sepia to dark sepia or dark reddish brown, often darkened with black-tipped hairs. The fur on the underparts is plumbeous, with white or silvery-white wash. The bicolored tail is dusky above and grayish below (Hall and Cockrum, 1953)."

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
not reported Banfield (1974) and Hall (1981); compiled by Ludwig (1984) 198–274 66–98 25–34 15–20
Virginia Ludwig (1984) head and body length for overwintered adults: 125–178 (males, n=86) and 125–165 (females, n=142) overwintered adults: 72.0–150.0 (males, n=86) and 68.0–140.0 (females, n=145)


Skull

From Ludwig (1984): "The skull is large, massive and angular. The wide zygomatic arches are strongly developed. The auditory bullae are reduced and not filled with spongy bones. The rostrum is slender; the incisive foramina are relatively small and constricted laterally. The paraoccipital processes are well developed, and the mandible also is constructed ruggedly (Banfield, 1974; Maser and Storm, 1970). The dentition is robust and the incisors protrude noticeably. The first lower molar (ml) normally contains a posterior transverse loop followed anteriorly by five closed triangles and a terminal transverse loop that is constricted in the middle. The last upper molar (M3) has an anterior transverse loop, a closed triangle on each side, and a short terminal loop (Bailey, 1900; Miller, 1896; Rhoads, 1894)."

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Similar species

From Ludwig (1984): "Except for the muskrat, Ondatra zibethicus, the water vole is the largest arvicoline rodent within its geographic range. In the field, young and overwintered adults can be distinguished from other voles by their large hindfeet (~23 mm). There are five plantar tubercules on the hindfeet (Miller, 1896) and both sexes have prominent flank glands (Quay, 1968)."

References

Bailey V. 1900. Revision of American voles of the genus Microtus. North American Fauna 17:1-88.

Banfield AWF. 1974. The mammals of Canada. Toronto (ON, CA): University of Toronto Press 438 pp.

Hall ER, Cockrum EL. 1953. A synopsis of the North American microtine rodents. University of Kansas publications, Museum of Natural History 5:375-499.

Ludwig DR. 1984. Microtus richardsoni. Mammalian Species (223): 1-6.

Maser C, Storm RM. 1970. A key to Microtinae of the Pacific Northwest (Oregon, Washington, Idaho). Oregon State Univ. Book Stores, Inc. Corvallis, 163 pp.

Miller Jr GS. 1896. Genera and subgenera of voles and lemmings. North American Fauna, 1.

Quay WB. 1968. The specialized posterolateral sebaceous glandular regions in microtine rodents. Journal of Mammalogy 49:427-445.

Rhoads SN. 1894. Description of a new genus and species of arvicoline rodent from the United States. Amer. Nat., 28:182-185.

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