61.

Masked Shrew

Sorex cinereus

French: Musaraigne cendrée / German: Amerikanische Maskenspitzmaus / Spanish: Musarana ceniza

Other common names: Cinereus Shrew, Common Shrew

Taxonomy. Sorex arcticus cinereus Kerr, 1792,

Fort Severn, Ontario, Canada.

Sorex cinereus is in the S. cinereus group and subgenus Otisorex. The S. cinereus group contains S. rohweri, S. longirostris, S. cinereus, S. fontinalis, S. lyelli, S. emarginatus, S. millet, S. preblei, S. hayden, S. pribilofensis, S. ugyunak, S. portenkoi, S. jacksoni, S. camtschaticus, and S. leucogaster . S. fontinalis has generally been considered a subspecies of S. cinereus but is considered a separate species here because the two species apparently overlap in distribution in Pennsylvania without interbreeding, although genetic data are needed to supportits species status. Recently, some Pacific Northwest populations have been described as a new species, S. rohweri, based on morphometric and genetic data. Sorex longipilis and S. milleri are included in S. cinereus genetically, but S. cinereus might represent multiple species. Recent genetic data have found various clades in S. cinereus from the Midwest, West, Southwest, Southeast, and East; S. longirostris being closest to the East clade; and S. milleri being closest to the Midwest clade. Sorex miller: might represent a relict population of S. cinereus, although morphometric data show that S. milleriis distinct; additional research is needed. Morphological data placed S. cinereus close to S. haydeni and S. fontinalis, although genetic data have not supported this. Two populations from south-western USA were closer to various other species, one from the central Rocky Mountains being closer to S. lyelli and the Beringian clade, while the other from northern Arizona and New Mexico was closer to S. haydeni and S. preblei . Subspecies acadicus is now considered a junior synonym of nominotypical cinereus based on recent morphometric studies. Subspecies here do not currently represent distributions of major clades in S. cinereus . Seven subspecies recognized.

Subspecies and Distribution.

S.c.cinereusKerr,1792—N&EAlaskaE&SthroughmuchofCanada(includingNewfoundland,NovaS.c.,andPrinceEdwardI)intothecontinentalUSAasfarSas NCNewMexicoandNGeorgia.

S. c. hollister: H. H. T. Jackson, 1925 —-W & C Alaska (USA).

S.c.lesueuriiDuvernoy,1842—NIllinoisEtotheSportionofMichiganandStoS Indiana(NEUSA).

S.c.miscixBangs,1899—LabradorandNEQuebec(ECanada).

S.c.magriculusGreen,1932—SNewJersey(NEUSA).

S.c.ohionensisBole&Moulthrop,1942—N&CMichigan,Ohio,andEPennsylvania(NEUSA).

S. c. streatori Merriam, 1895 — SE Alaska to SW British Columbia along the full Pacific coast of W Canada.

Descriptive notes. Head-body 42-67 mm, tail 29-50 mm, hindfoot 10-5-13 mm; weight 2-5-6 g. The Masked Shrew is relatively small, similar to the South-eastern Shrew ( S. longirostris) and the Maryland Shrew ( S. fontinalis). Dorsum is dark brown, sometimes with darker dorsal line and paler sides, and their entire body is grayer in winter. Venter is distinctly paler than dorsum, being grayish brown with silvery tinge. Tail is c.65-80% of head-body length, narrow, and distinctly bicolored, being dark brown above and nearly white below; tip has distinct black tuft of hair 2-3 mm long, unlike the Prairie Shrew ( S. haydeni) that has brown tip on tail. There are five unicuspids,first four are approximately the same size, becoming slightly smaller from first to fourth, and fifth is significantly smaller butstill visible in tooth row; some individuals have a third unicuspid that is smaller than fourth, especially in subspecies ohionensis. Teeth are pigmented dark red, being darker than that of the South-eastern Shrew. Chromosomal complement has 2n = 66 and FN = 70.

Habitat. Wide variety of habitats including arid grasslands, woodlands, marshlands, and tundra. The Masked Shrew is a habitat generalist in temperate and polar regions and is often one of the most common shrews and small mammals in an area. Although Masked Shrews can be found in more arid habitats, they often require areas with moisture and are captured at highest densities in grass-sedge marshes, willow-alder fens, heath moss bogs, various swamp habitats, and some shrublands and prairies and are less common in xeric and tundra habitats although they are still present. When sympatric with the Prairie Shrew, Masked Shrews stay more in forested and woodland habitats, and Prairie Shrews stay in open grassland habitats.

Food and Feeding. Masked Shrews feed often and voraciously like most other species of shrews, only being able to survive for a few hours without food because of their high metabolic rate. A captive individual (3-6 g in weight) feeding on liver ate c.11-7 g of food/day over a seven-day period, which indicated that c.3-3 times their own body weight must be eaten each day. Otherstudies with captive individuals feeding on liver found values of 1-3-3-8 g/day, indicating that they more often eat about their weight in food. Masked Shrews eat various small invertebrates and vertebrates, including adult and larval insects, centipedes,snails, slugs, worms, sowbugs, spiders, harvestmen, salamanders, possibly carrion, seeds on occasion, and small amounts of Endogone fungus. Based on data from the eastern USA and Nova Scotia, beetles and various insect larvae usually made up the largest proportion of diets of Masked Shrews (65-3%), while small vertebrates (including salamanders; 7-1%), centipedes (6-8%) worms (4-3%), mollusks (1-4%), and sowbugs (12%) made up smaller proportions of diets. Many insect larvae are eaten, especially beetles, moths, and flies, although adult forms of insects are also eaten on occasion, especially beetles. Earthworms do not make up a very significant proportion of their diets, indicating foraging is more epigeal than hypogeal because their diets consist largely of epigeal prey (e.g. beetles). Nevertheless, captive individuals are known to investigate small holes and burrows and will pull worms out if they are found. When foraging, Masked Shrews generally rummage through leaf litter and vegetation, often disappearing under the cover. Food is occasionally cached in side compartments in tunnels.

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Breeding. Breeding of Masked Shrews primarily occurs in March-September, although there have been reports of births throughout the year including mid-winter in Nova Scotia. Pregnant females have been reported from early April until August. Females can breed 1-6 times/season, which is abnormally high for shrews, and some young can breed in the same season they are born, although they more often breed the following year. Gestation lasts c.18 days, and litters generally have 2-10 young (average 6-7 young but 4-9 in some regions). Newborns average 0-28 g and are 12-14 mm from crown to rump. Young are weaned at c.3 weeks, and sexual maturity is reached at ¢.20-26 days old, looking adult-like at c.20 days old and leaving the nest at ¢.27 days old. Caravanning has been observed after young are able to leave the nest, althoughit only lasts c.5 days. Young adults often start appearing outside the nest in June and stop appearing in about September, although there are reports from before June and after September. Masked Shrews generally do not live longer than 19 months, although some individuals have been reported to live up to 30 months, surviving for two breed-Ing seasons.

Activity patterns. Activity of Masked Shrews occurs day and night in short bouts of foraging and other activity, with longer periods of rest between them; they are usually most active throughout the night. During rest periods, their metabolic rate is depressed, and they often sleep. They are also most active during moist weather and with increased cloud cover and rain. Nests are generally found under rotten logs, rocks, or human structures and consist of balls of woven dry grass ¢.4—6 cm in diameter, with openings c¢.2-3 cm in diameter. Leaves and plastic have been used to line nests, and there are often exit tunnels attached to the nest.

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Movements, Home range and Social organization. Masked Shrews use aboveground runways and narrow underground tunnels (c.2 cm in diameter) to get around and will excavate their own tunnels or use tunnels created by other small mammals. They are territorial and generally solitary when not breeding or rearing young, although four adult individuals have been found sharing a tunnel system, indicating that they might be somewhat gregarious in winter and during breeding. Males generally abandon their home ranges during breeding to travel and find females, and females retain and expand their home ranges. Home ranges generally decrease in size as density increases. Densities vary throughout the year and by location ranging from 2-5-27 ind/ ha in Ohio (7-6-10 ind/ha in white cedar and black spruce forests) and 2-13 ind/ ha in Pennsylvania. In a seven-year study, densities were 1-23 ind/ha in south-eastern Manitoba, being lowest in spring and highest in late summer/early autumn, correlated with when juveniles/subadults enter the population. Mortality rates are high: c.80% of young die before reaching sexual maturity, and ¢.50% of the surviving shrews die during the next five months. At high densities, some individuals call to each other, then meet to have a short territorial dispute before running away from each other and then calling again after several minutes. These calls have been observed over relatively large areas of c.900 m?. Like most temperate species of shrews, body mass decreases during winter and rapidly increases in spring.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Masked Shrew has a very wide distribution and faces no major threats, being able to survive in highly disturbed habitats. Fossil record shows that it once occurred as far south as north-eastern Mexico. It is one of the most common species of small mammals throughout its distribution and is common around agricultural settlements and even some urban areas. Effects of the bacterial insecticide Bacillus thuringiensis have been noted for the Masked Shrew; when it is used, males in a population decreased due to emigration, but they were not negatively affected by the application.

Bibliography. Anderson (1981), Bellocq & Smith (1994), Bellocq et al. (1992), Blossom (1932), Brown (1967), Cassola (20161), Demboski & Cook (2003), Forsyth (1976), French (1984), George (1988), Hope et al. (2012), Innes et al. (1990), Ivanitskaya & Kozlovsky (1985), Kirkland (1976, 1977a, 1977b), Merritt (1995), Moore (1949), Morrison et al. (1959), Pruitt (1954), Stewart et al. (1993), Vickery & Bider (1978), Whitaker (2004), Whitaker & Schmeltz (1973), Woodman (2018), van Zyll de Jong (1980), van Zyll de Jong & Kirkland (1989).