139.

Beach Vole

Microtus brewer

French: Campagnol de Muskeget / German: Strandw (ihimaus / Spanish: Topillo de Muskeget

Other common names: Beach Meadow Mouse, Beach Mouse

Taxonomy. Arvicola brewer: Baird, 1858, Muskeget Island, west of Nantucket Island, Massachusetts, USA.

Based on mtDNA and nDNA, M. brewer: is minimally distinctive from M. pennsylvanicus and nested in its eastern clade. The current population of M. breweri was founded from 26 relict individuals that survived depredation by introduced feral cats and were reintroduced to the main part of Muskeget Island in 1893. Monotypic.

Distribution. Muskeget I, Massachusetts, USA.

Descriptive notes. Head—body 124-155 mm (males) and 130-146 mm (females), tail 45-60 mm (males) and 35-55 mm (females), hindfoot 22-25 mm (males) and 22-25 mm (females); weight 45-1-62-9 g.

Males are larger than females. The Beach Vole differs from the Meadow Vole ( M. pennsylvanicus) by having larger skull and longer narrower braincase. Nasals are wider anteriorly, and interparietal is longer. Dorsal pelage is paler, longer, and coarser than the Meadow Voles, and is buffy gray, with scattered brownor back-tipped hair; sides are paler. Tailis bicolored, with brown or black above and off-white below. It has a patch or blaze ofwhite fur on forehead, or less commonly on chin or throat (¢.25% of individuals). Chromosomal complement of the Beach Vole is nearly identical to that of the Meadow Vole, and both species have 46 chromosomes.

Habitat. Variety of plant associations, dominantly Ammophila breviligulata ( Poaceae) where runways are built, identified by grass clippings. The Beach Vole is also associated with Rhus radicans ( Anacardiaceae), Rosa rugosa ( Rosaceae), Juniperus virginiana ( Juniperaceae), and Myrica pennsylvanica (Myricaceae) . It burrows and uses tunnels, and nests are constructed aboveand belowground.

Food and Feeding. Beach Voles eat tender shoots of beach grass in warm months and cache grass stems in wet sand to eat in winter.

Breeding. Beach Voles breed from spring to autumn, with young born in nests in underground burrows or under debris or driftwood cover. Females typically produce multiple litters of 4-5 young/year. Compared with Meadow Voles, Beach Voles reach sexual maturity later and have lower pregnancy rates and smaller litter sizes.

Activity patterns. Activity patterns of Beach Voles vary temporally between sexes.

Movements, Home range and Social organization. In contrast to most other microtine voles, densities of Beach Voles have fewer and smaller fluctuations. Because it is an island species, lack of a dispersal sink and fewer predators may contribute to relatively stable populations, although density fluctuates from c.5 ind/ha in low years to c.15 ind/ha in peak years. A nearly sixfold fluctuation in density also has been reported, and very early reports suggested high densities of Beach Voles. Adult sex ratios vary little between years, and adult male and adult female daily home ranges are similar.

Status and Conservation. Classified as Vulnerable on The IUCN Red List. The Beach Vole occurs in less than 2:6 km?

Bibliography. Miller (1896b), Modi (1987), Musser & Carleton (2005), Rothstein & Tamarin (1977), Tamarin (1977a, 1977b), Tamarin & Kunz (1974), Tamarin et al. (1987), Zwicker (1989).