|Scientific Name:||Microtus breweri|
|Species Authority:||(Baird, 1858)|
|Taxonomic Notes:||According to Modi (1986), karyotypic analysis indicates that M. breweri should be synonymized with M. pennsylvanicus; morphological differences between the two are attributable to island effects in breweri. Microtus breweri and M. pennsylvanicus are marginally distinct electrophoretically. Moyer et al. (1988) presented cranial and dental evidence supporting recognition of M. breweri as a species distinct from M. pennsylvanicus. Jones et al. (1992), Baker et al. (2003), and Musser and Carleton (in Wilson and Reeder 1993, 2005) recognize M. breweri as a distinct species.|
|Red List Category & Criteria:||Vulnerable D2 ver 3.1|
|Assessor(s):||Linzey, A.V. & NatureServe (Hammerson, G.)|
|Reviewer(s):||Amori, G. (Small Nonvolant Mammal Red List Authority) & Chanson, J. (Global Mammal Assessment Team)|
Listed as Vulnerable because it is now only known from only one island (historically it was known from two other neighbouring islands), it has an intrinsic tendency to undergo wide population fluctuations, and although there are no threats currently identified, the species' habitat is not protected and so there is the potential for detrimental human impacts on the habitat in the future.
|Range Description:||This species' range is limited to Muskeget Island, off the west coast of Nantucket, Massachusetts, United States (Tamarin and Kunz 1974). Historically this vole also occurred on nearby Adams and South Point islands, which can be regarded as part of Muskeget Island in the broad sense. Muskeget Island has changed shape, size, and position over time; it has moved more than 1,000 feet eastward since the 1800s (Surfrider Foundation, State of the Beach 2005; www.surfrider.org).|
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||This species occurs only on one island. The population reportedly fluctuates between about 3,000 and 10,000 individuals but evidently does not exhibit regular long-term (3-4 year) cycles (Tamarin 1977). Density is about 12 per acre in low years, 37 per acre in peak years (density varied 5.8 fold over five years in another study).|
|Habitat and Ecology:||
The principal habitat for these voles are meadows dominated by beach grass (Ammophilia breviligulata) and poison ivy (Rhus radicans) (Hafner et al. 1998). They burrow in coarse loose sand, also on loose soil under or near any shelter (e.g., driftwood). Young are born in nests in underground burrows or under other cover. They breed from spring to fall. Gestation lasts about one month. Individual females produce up to several litters of four to five young per year. Most live probably less than one year.
Home range is less than one acre. Cats, short-eared owl, northern harrier, and common garter snake are predators. Beach voles feed on beach grass stalks. They may also utilize seeds, and leaves of various plants and some insects. They are probably chiefly diurnal.
|Major Threat(s):||There are no known threats to the species at present, but its very restricted range makes it vulnerable to threatening processes. Potential threats include introduced predators, habitat disruption by humans, and island erosion.|
|Conservation Actions:||It is not known whether any occurrences are appropriately protected and managed. Ideally conservation measures would involve protection of Muskeget Island by direct purchase or management agreements with landowners.|
|Citation:||Linzey, A.V. & NatureServe (Hammerson, G.) 2008. Microtus breweri. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 18 April 2015.|
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