Western harvest mouse (Reithrodontomys megalotis) COSEWIC assessment and update report: chapter 10

Existing Protection or Other Status Designations

The extensive distribution of western harvest mice (R. megalotis) throughout most of the US and Mexico results in this species receiving a global rank of G5 and a national (US) rank of N5, which implies that this mouse is demonstrably widespread, abundant, and secure throughout most of North America, including Mexico (NatureServe 2005). The limited distribution within Canada results in a Canadian national rank of N2N3 (imperiled to uncommon, generally consisting of six to 100 extant occurrences; NatureServe 2005). As a result it was previously assessed by COSEWIC in April 1994 as Special Concern in BC and Data Deficient in Alberta.

British Columbia

The widespread distribution of the BC subspecies of western harvest mice (R. m. megalotis) throughout the western US and Mexico results in this infraspecific taxon receiving a global rank of T5 (very common), and a sub-national rank of S4S5 (frequent to very common) within Washington, the only state adjacent to its range within BC (NatureServe 2005). In BC, because of the limited distribution and apparent rarity, this mouse is ranked as S2S3 (imperiled to uncommon, generally consisting of six to 100 extant occurrences; British Columbia Conservation Data Centre 2005). The widespread use of road edge and disturbed habitats kept the subspecies from being uplisted further (L.R. Ramsay; pers. comm.). The western harvest mouse is on the provincial Blue List and is therefore considered Vulnerable (Cannings et al. 1999, British Columbia Conservation Data Centre 2005). This species is also protected by the provincial Wildlife Act; collecting or live-trapping requires permits.

Alberta

Although the distribution of the Alberta subspecies of western harvest mice (R. m. dychei) is widespread throughout the central US, this infraspecific taxon receives a global rank of TNR (rank not yet assessed), likely due to a lack of data at the subspecies level (NatureServe 2005). Within Montana, the only state adjacent to its range within Alberta, this subspecies receives a sub-national rank of S4 (apparently secure but may have restricted distribution; NatureServe 2005). In Alberta, because of the limited distribution and apparent rarity, this mouse is ranked as S1 (critically imperiled and known from five or fewer extant occurrences; NatureServe 2005). A lack of data has resulted in this subspecies being classified by the provincial government as Status Undetermined (Province of Alberta 2000). In Alberta, the mouse is protected by the provincial Wildlife Act as a non-game species.

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