Sorex navigator

78. Western Water Shrew Sorex navigator French: Musaraigne de Washington / German: Westliche Wasserspitzmaus / Spanish: Musgano occidental Taxonomy. Neosorex navigator Baird, 1858, “ Fort Vancouver, W. T. [= Washington Territory],” Washington, USA. Sorex navigator is in the S. palustris group and subgenus Ofisorex; it is sister to S. bendiru. It was previously included in S. palustris, although genetic and morphometric studies have justified its distinct status. There is apparent hybridization between it and S. palustris where their distributions meet in Alberta and British Columbia. Distribu- tional limits between the two species are uncertain, and additional studies are needed. Distributional limits between S. palustris and S. navigator are still very uncertain, and because of this, much of the ecological data cannot be reliably attributed to one species. Thus, all ecological data for S. albibarbis, S. navigator, and S. palustris are presented under S. palustris here. Two subspecies recognized. Subspecies and Distribution. S.n.navigatorBaird,1858—NorthAmericanCordilleraandWesternCoastalRegionsinSAlaska,WCanada,andWUSA;specificdistributionuncertain. S. n. brooksi R. M. Anderson, 1934 — Vancouver I (SW Canada). Descriptive notes. Head—body 56-85 mm, tail 62-79 mm, hindfoot 17-20-5 mm; weight 6-5-21-5 g. The Western Water Shrew is a large semi-aquatic shrew, very similar to the American Water Shrew (S. palustris), although it is smaller in size on average and has a longertail. Pelage is highly variable; dorsum is generally blackish brown and occasionally flecked with white, giving it grizzled appearance. Venteris silvery white to buffy brown. Occasionally, there is a nearly all blackish form, with lighter throat and chest, although this is rare. Feet are large and broad, and hindfeet are partially webbed and have small white hairs protruding on their sides. Tail is long, somewhat laterally flattened, and bicolored, being dark blackish brown above and lighter below, with small tip of fur at end. Skull has relatively longer unicuspid toothrow, smaller first unicuspid, and longer rostrum compared with the American Water Shrew. Teeth are pigmented dark red. There are five unicuspids, third is smaller than fourth, and fifth is much smaller. Habitat. Around streams, ponds, lakes, swamps, marshes, and bogs. Western Water Shrews are most common around small, fast-moving streams surrounded by dense overhanging riparian vegetation and rocks. Although they are most commonly associated with water, individuals have been captured far from water sources, which probably represents dispersing individuals. Food and Feeding. Diets of Western Water Shrews are probably similar to those of the American Water Shrew. Breeding. Reproduction of the Western Water Shrew is probably similar to that of the American Water Shrew. Activity patterns. Western Water Shrews are semi-aquatic, with activity patterns probably similar to those of the American Water Shrew. Movements, Home range and Social organization. The Western Water Shrew is probably similar to the American Water Shrew. Status and Conservation. Not assessed on The IUCN Red List. The Western Water Shrew is common and widespread, butit is threatened by localized habitat destruction and water pollution. Bibliography. Beneski & Stinson (1987), Brown (1967), Catania (2006), Conaway (1952), Conaway & Pfitzer (1952), Cook et al. (1997), Craig et al. (2001), Gusztak & Campbell (2004), Himes & Kenagy (2010), Hope et al. (2014), Mycroft et al. (2011), Nagorsen et al. (2017), Sorenson (1962).

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