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Alien invaders: recent establishment of an urban population of house mice (Mus musculus) in the Yukon.

Key words: alien species, House Mouse, invasive species, Mus musculus, Yukon


The House Mouse (Mus musculus) is an Old World rodent that has become one of the most widespread mammals. Originally native to northern India, human activities have inadvertently facilitated their colonization of all continents except mainland Antarctica. They are among the most successful alien and invasive mammals (Clout and Russell 2007). Typically they are found living commensally with humans, but House Mice may also establish populations in natural environments (Schwarz and Schwarz 1943; Nagorsen 2005). House Mice may have significant negative impacts on humans and native species, particularly when their populations reach high densities, thus they are of considerable management interest.

House Mouse populations are not well known in northwestern Canada and Alaska. For example, MacDonald and Cook (2009) noted that "(i)nformation on the distribution of the House Mouse In Alaska is nearly nonexistent", with most records coming from coastal populations. In Yukon, Canada, Young man (1975) reported commensal House Mice in Whitehorse (UTM Zone 8V, 496905E, 6731729N, NAD83; n = 3 specimens) and Dawson City (UTM Zone 7W, 576597E, 7104462N, NAD83; n = 17 specimens). In a recent review, however, Slough and Jung (2007) reported no observations or specimens from the Yukon since the 1970s, and described the species' status in the Yukon as hypothetical. Herein, we document recent records and evidence of breeding for House Mice in an urban area of southern Yukon.

In autumn 2010, we obtained an adult male House Mouse trapped in Whitehorse by a local resident. To determine if a breeding population existed, we solicited the public by radio and television to submit small mammals legally trapped in their residences. Specimens submitted were identified using the keys provided by Nagorsen (2005).

Between September 2010 and February 2012, we obtained 250 small mammals representing 5 species from 6 communities. Of the 250 submissions, 111 were House Mice. All were from Whitehorse, the largest community in the territory. The House Mice were collected in the downtown and suburban areas, where they were associated with high densities of buildings. No House Mice were obtained from rural residential areas where housing density is substantially reduced and embedded in a matrix of natural areas. Most House Mice were taken during September to November when homeowners are most actively trapping small mammals; however, exact dates of capture were often unknown. House Mice were collected both inside occupied buildings and outside near unoccupied buildings (for example, sheds). Deer mice (Peromyscus spp.) were trapped at 2 of the 17 locations with House Mice in Whitehorse, demonstrating that these species cohabit some buildings during autumn and winter. Our House Mouse sample consisted of 2 color variants: 75 (68%) were of typical uniform dark coloration and 36 (32%) were bicolored, with white on the ventral side. Voucher specimens will be archived at the University of Alaska Museum (Fairbanks, Alaska).


Our collections extended over 2 winters, providing evidence for over-winter survival. The sample had more males (n = 60; 54%) than females (n = 51; 46%). Body mass distribution suggested that all age-classes were represented, including juveniles (Fig. 1). Of the 60 males, 36 (60%) were reproductive with scrotal testes; 10 females (20%) were lactating and 8 (16%) were pregnant, confirming reproduction.

Our collections demonstrate the existence of an established urban population of House Mice in Whitehorse, where they appear to be common. The cold climate of northern North America may not be inhospitable to this adaptable mammal. Webb and others (1997) suggested that feral House Mice were well adapted to the cold climate of sub-Antarctic islands. Outside of North America, commensal House Mouse populations have been reported from locations at greater latitudes (for example Tromso, Norway; Jones and others 2010) and with colder climates (for example Yakutsk, Russia; Ruvinsky and others 1991). However, the Whitehorse population may represent the most northerly House Mouse population in North America. Although individuals were previously collected in more northern communities in Yukon, Northwest Territories and Alaska (Porsild 1945; Youngman 1975; MacDonald and Cook 2009), they are not believed to represent established populations (Slough and Jung 2007; BK Jacobson and LE Olson, University of Alaska Museum, pers. comm.).

How House Mice were introduced to the Yukon is unknown, but typically they are inadvertently transported in shipments of food or other goods (Schwarz and Schwarz 1943; Brown 1953). We suspect that some individuals are routinely introduced to northern communities through unintentional human transport, but most colonizations fail to become established. The 40 y hiatus in records from the Yukon suggests that earlier introductions did not result in established populations (Slough and Jung 2007), and that the extant urban population is from a more recent colonization. Monitoring is necessary to document the persistence of the urban House Mouse population in Whitehorse, and to determine if they are established in other communities or natural environments in the region.

Acknowledgments.--We thank the many Yukon residents that submitted specimens, particularly CD Eckert and H Grunberg for their series. We thank JA Cook, BK Jacobsen, V Loewen, LE Olson, and BG Slough for interesting discussions about House Mouse records in Yukon and interior Alaska. S Carriere and DF McAlpine kindly provided thoughtful comments that improved this manuscript.


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Yukon Department of Environment, PO Box 2703, Whitehorse, YT YIA 2C6; (TSJ, PMK, OEB); Mammalia Biological Consulting, 4268 Metchosin Road, Victoria, BC V9C 3Z4 (DWN). Submitted 9 March 2012, accepted 28 May 2012. Corresponding Editor: Paul Cryan.
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Article Details
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Title Annotation:GENERAL NOTES
Author:Jung, Thomas S.; Nagorsen, David W.; Kukka, Piia M.; Barker, Oliver E.
Publication:Northwestern Naturalist: A Journal of Vertebrate Biology
Article Type:Report
Geographic Code:1CANA
Date:Dec 22, 2012
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