Sorex arcticus Kerr 1792

26. Arctic Shrew Sorex arcticus French: Musaraigne nordique / German: Arktische Spitzmaus / Spanish: Musarafa del Artico Other common names: Black-backed Shrew, Saddle-back Shrew Taxonomy. Sorex arcticus Kerr, 1792, “ Hudson Bay ” Ontario, Canada. Sorex arcticus is currently included in the arcticus group in the subgenus Sorex along with S. maritimensis, which was originally included in S. arcticus as a subspecies. Additional research is needed to validate subspecies. Two subspecies recognized. Subspecies and Distribution. S.a.arcticusKerr,1792—Canada,fromCYukonEtoEQuebecandStoNWNorthDakota,USA. S. a. laricorum H. H. T. Jackson, 1925 — NC USA (most of North Dakota, NE South Dakota, Minnesota, Wisconsin, and NW Michigan). Descriptive notes. Head—body 68-89 mm, tail 36-48 mm, ear 7-8 mm, hindfoot 13— 16 mm; weight 5-13 g. The Arctic Shrew is medium-sized. Pelageis tricolored, being dark brown to black on back, pale dusky brown on sides, and whitish on belly; dorsum, sides, and venter are sharply demarcated from each other. Pelage is paler in summer and darker and thicker in winter. Feet are dark; ears are short and barely extend past fur. Tail is ¢.50% of head-body length and indistinctly bicolored, being dark brown above and lighter below.Juveniles are significantly darker, with brown venter and sides. Tooth ridges (except for on unicuspids as in other members of the subgenus Sorex) are pigmented dark red, and there are five unicuspids gradually getting smaller from first to fifth, which is significantly smaller than the fourth. Chromosomal complement has 2n = 28 (females) or 29 (males) and FN = 38. Habitat. Grass-sedge marshes, wet meadows, and various other moist areas in boreal forests; less common butstill present in tamarack-spruce bogs and cedar swamps. The Arctic Shrew seems to compete with the Masked Shrew (S. cinereus) where they are sympatric, and as the population of one species increases, the other decreases. Food and Feeding. Diets of Arctic Shrews consist almost exclusively of various insects, but larval larch sawflies (Pristiphora erichsonii) tend to be a major component seasonally, making up ¢.70% of diets in August-November. They rely on various other insects, including grasshoppers, throughoutthe rest of the year when food is scarce, becoming more opportunistic. They feed primarily terrestrially but will occasionally climb branches and shrubs tojump on prey from above. Two subadults were seen attacking grasshoppers by climbing up branches to jump on them in the morning when temperatures were low (6°C) and grasshoppers were sluggish; 33 of 37 attacks were successful. They occasionally eat various aquatic insect larvae because they reside close to streams and bogs. Captive individuals ate dead voles,fly pupae, and mealworms. Estimated minimal metabolic rate is 4-7 kcal/day. Breeding. Reproduction of Artic Shrews occurs February—August in Wisconsin but becomes more restricted in northern regions, although they generally breed from midwinter to mid-summer. They are promiscuous, and males abandon their home ranges during the breeding season to mate with as many females as possible. Gestation lasts c.3 weeks, and lactation lasts c.4 weeks. Litters have 4-9 young (average seven), and females average c.3 litters/year. First young generally start appearing in traps in July, and young born earlier in the season can breed in the same season they were born. Maximum longevity is c.18 months, which might be shorter than other species of Sorex. Activity patterns. The Arctic Shrews are active throughout the day; they are least active from 06:00 h to 10:00 h and most active throughout the night. They switch between activity and resting throughout the day and generally sleep during rest periods. They are terrestrial and use vision to hunt and navigate. They build small globular nests aboveground but under logs, rocks, or other large objects with space under them. Movements, Home range and Social organization. Arctic Shrews are solitary except when mating and rearing young (which is done only by the female). During the first month of life, mortality rate is ¢.50% and about one-seventh of all mortality occurs in the first month after young leave the nest. About 80% of mortality occurs before young reach sexual maturity, with only 15-20% breeding in the next season. Densities were estimated at 8-6 ind/ha in October in Wisconsin and 4-1-5-1 ind/ha in July and 7-3-7-8 ind/ha in September in south-eastern Manitoba; they generally are 1-4 ind/ ha. Home ranges have been recorded at c.1 ha, although this varies throughout the year and probably over their distribution. Status and Conservation. Classified as Least Concern on The IUCN Red List. The Arctic Shrew has a wide distribution, is considered common, and seems to face no major conservation threats. Bibliography. Baird et al. (1983), Buckner (1964, 1966, 1970), Cassola (2016k), Clough (1963), Fumagalli et al. (1996), Jackson (1928), Junge & Hoffmann (1981), Junge et al. (1983), Kirkland & Schmidt (1996), Kozlovsky (1971), Perry et al. (2004), Volobouev (1989), Volobouev & van Zyll de Jong (1988), van Zyll de Jong (1983).

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