Species Profile

Western Harvest Mouse megalotis subspecies

Scientific Name: Reithrodontomys megalotis megalotis
Other/Previous Names: Western Harvest Mouse (British Columbia population)
Taxonomy Group: Mammals
COSEWIC Range: British Columbia
COSEWIC Assessment Date and Status Change: November 2019
COSEWIC Status: Endangered
COSEWIC Status Criteria: B1b(iii)c(iv)+2b(iii)c(iv)
COSEWIC Reason for Designation: This tiny mouse occurs at the northern edge of its distribution within the Okanagan and Similkameen valleys of British Columbia, and is one of two designatable units of the species in Canada. It is among Canada’s shortest-lived mammals. This species demonstrates extreme fluctuations in the number of mature individuals over time, increasing vulnerability to disturbances when populations are at a low in spring and early summer. The species’ limited distribution, extreme fluctuations, and habitat loss are the reasons for designation. Change in status from Special Concern to Endangered is the result of inclusion of extreme fluctuations in the latest assessment. Continued urban and agricultural expansion threaten the persistence of this mouse.
COSEWIC History of Status Designation: Designated Special Concern in April 1994 and in April 2007. Status re-examined and designated Endangered in November 2019.
SARA Status: Schedule 1, Special Concern
Date of Listing (yyyy-mm-dd): 2009-03-05

Please note that this information is provided for general information purposes only. For the most up to date and accurate list of species listed under the Species at Risk Act, please see the Justice Laws Website.

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Image of Western Harvest Mouse megalotis subspecies

Western Harvest Mouse megalotis subspecies Photo 1

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Description

The Western Harvest Mouse is one of the smallest mice in North America; it averages 13.6 cm in length, half of which is its tail. This brownish mouse has a dark dorsal stripe that runs from forehead to tail. The hindfeet are white, its flanks and cheeks are a buff-coloured and the fur on its belly can be white to deep grey. Its long, sparsely-haired tail is grey above, whitish below. The prominent ears are hairless.   This rodent is easily confused with the Deer Mouse and the House Mouse, two larger and more common species. However, the juvenile Deer Mouse is most often grey in colour and the House Mouse's tail is completely bare.

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Distribution and Population

The Western Harvest Mouse is widespread throughout western North America, from southern Canada down to central Mexico. In Canada, it is restricted to the grasslands of south-central British Columbia and southern Alberta. The Alberta and British Columbia populations, separated by the Rocky Mountains, are of the dychei and megalotis subspecies, respectively.   In British Columbia, the Western Harvest Mouse megalotis subspecies occurs throughout the Okanagan Valley, as far north as Vernon, and in the Similkameen Valley, as far north as Keremeos. The mouse has not been captured in central Okanagan near Kelowna, suggesting that the Vernon population is isolated from populations to the south. The species is also absent from adjacent valleys, including the Thompson River and Kettle River valleys. However, low trapping success makes the absence of records an unreliable means of assessing distribution.   In contrast to the US, where the Western Harvest Mouse is a dominant member of grassland small mammal communities, this species is rather rare in Canada, typically comprising less than 10% of such communities. However, population densities as high as 80 individuals/hectare have been reported in British Columbia. Western Harvest Mouse populations appear to peak in late fall or early winter and decline to low levels in midsummer. There are no data available on population size or trends at either a provincial or national level.

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Habitat

Little is known about the detailed habitat requirements of the Western Harvest Mouse, but the species is reported to prefer habitats characterized by thick herbaceous cover of tall grasses or shrubs.   The British Columbia population appears restricted to very hot, dry valley bottoms where bitterbrush and big sagebrush grow. It is found in various habitats, including dry gullies with dense shrub cover that border grasslands, old fields, apple orchards, Ponderosa pine forests and grassy areas bordering cultivated fields.   Although preferring herbaceous cover in habitats without heavy grazing, the Western Harvest Mouse megalotis species is found in grazed habitats in British Columbia, as long as there is enough cover provided by shrubs such as bitterbrush or sagebrush.   Since the 1930s, the extent of available habitat for the Western Harvest Mouse in the Okanagan Valley has been declining because of the combined effects of cattle grazing, agriculture and urbanization. Its principal natural habitat, as well as old fields, are declining. Furthermore, old apple orchards where the mouse has been caught are being converted into vineyards. The disappearance rate of its habitat is accelerating.

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Biology

In British Columbia, the breeding season extends from March through November. Females can breed at four months of age and have up to five litters per season with an average litter size of three. The Western Harvest Mouse builds a small grass nest on the ground or in shrubs up to 1 m above ground. It does not build burrows, but sometimes uses burrows of other small mammals. The Western Harvest Mouse appears to be able to enter torpor to cope with cold temperatures. This dormant state, where vital functions slow down, may be essential to the survival of Canadian populations. Some researchers speculate that they hibernate, although this does not appear to occur in southern British Columbia as this species was observed throughout the year. This nocturnal mouse is omnivorous; it mainly feeds on seeds and insects, such as caterpillars and moths, but also on new plant growth and flowers. In Canada, birds of the Strigidae family, such as the Northern Saw-whet Owl, are the only officially confirmed predators of the Western Harvest Mouse, but other likely predators include prairie rattlesnakes, hawks, jays, shrikes, raccoons, foxes, weasels, skunks, badgers and coyotes. Although the Western Harvest Mouse can live naturally for 18 months, most do not live past six months.   The Western Harvest Mouse is sometimes in competition with rodents of similar size. In British Columbia, the Montane Vole may be an important competitor.

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Threats

Habitat fragmentation and loss caused by grazing, cultivation or other agricultural activities, along with urban development, are likely the most significant threats to populations in Canada.   The Western Harvest Mouse's habitat is mostly threatened by cattle and horse grazing, agriculture and urbanization. In British Columbia, conversion of grasslands to orchards, cultivated fields, and more recently, urban development and vineyards, has eliminated large areas of shrub-steppe habitats important to this species. The use of roadside habitats and habitats along cultivated fields may be particularly important for the dispersal of this species among suitable habitat fragments.   The Western Harvest Mouse is susceptible to habitat change, such as the disappearance of herbaceous cover and food, resulting from fire, but populations can recover quickly, provided there is suitable unburnt habitat nearby.   The creation of new roads may represent a significant barrier to dispersal and movement of the Western Harvest Mouse.   Finally, the use of pesticides to control vole and pocket gopher populations in old field and orchard habitats in British Columbia may have significant impacts on local populations of the Western Harvest Mouse. However, orchards are not the species' preferred habitat; thus, mortality from poisoning is assumed to be low.

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Protection

Federal Protection

The Western Harvest Mouse megalotis subspecies is protected under the federal Species at Risk Act (SARA). More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.

Provincial and Territorial Protection

To know if this species is protected by provincial or territorial laws, consult the provinces' and territories' websites.

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Documents

PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.

12 record(s) found.

COSEWIC Status Reports

  • COSEWIC assessment and status report on the Western Harvest Mouse Reithrodontomys megalotis, megalotis subspecies and dychei subspecies, in Canada (2020-10-21)

    Western Harvest Mouse (Reithrodontomys megalotis) has a body mass of approximately 11 g and averages 136 mm in total length, half of which is its tail. This brownish mouse has a faint dark dorsal stripe which runs the length of its body from head to tail, and has whitish fur on its belly. Western Harvest Mouse has prominent naked ears, a tail that is sparsely furred and white feet. It is similar in appearance to the larger and more common Deer Mouse and House Mouse; however, the juvenile Deer Mouse is most often grey in colour and the House Mouse has a tail that is completely naked. Note: This COSEWIC assessment was received by the Minister on September 2, 2020.
  • COSEWIC assessment and update status report on the Western Harvest Mouse Reithrodontomys megalotis megalotis and Reithrodontomys megalotis dychei in Canada (2007-08-29)

    The western harvest mouse (Reithrodontomys megalotis) has a body mass of approximately 11 g and averages 136 mm in total length, half of which is its tail. This brownish mouse has a faint dark dorsal stripe which runs the length of its body from head to tail, and has whitish fur on its belly. This species has prominent naked ears, a tail that is sparsely furred and white feet. It is similar in appearance to the larger and more common deer mouse and house mouse; however, juvenile deer mice are most often grey in colour and house mice have tails that are completely naked.

Response Statements

  • Response Statement - Western Harvest Mouse megalotis subspecies (2007-12-04)

    This subspecies has a limited range, and a small extent of occurrence and area of occupancy. However, the extent of occurrence and area of occupancy appear to be constant. Its principal native habitat in the Okanagan as well as old fields is declining. Furthermore, old apple orchards where the mouse has been caught are being converted to vineyards. Dispersal distance is limited and the likelihood of rescue effect is small. Extensive sampling has revealed the occurrence of the mouse at more localities. 63,000 hectares of suitable habitat is protected.
  • Response Statement - Western Harvest Mouse megalotis subspecies (2020-12-02)

    This tiny mouse occurs at the northern edge of its distribution within the Okanagan and Similkameen valleys of British Columbia, and is one of two designatable units of the species in Canada. It is among Canada’s shortest-lived mammals. This species demonstrates extreme fluctuations in the number of mature individuals over time, increasing vulnerability to disturbances when populations are at a low in spring and early summer. The species’ limited distribution, extreme fluctuations, and habitat loss are the reasons for designation. Change in status from Special Concern to Endangered is the result of inclusion of extreme fluctuations in the latest assessment. Continued urban and agricultural expansion threaten the persistence of this mouse.

Management Plans

Orders

COSEWIC Annual Reports

  • COSEWIC Annual Report - 2007 (2007-08-30)

    2007 Annual Report to the The Minister of the Environment and the Canadian Endangered Species Conservation Council (CESCC) from the Committee on the Status of Endangered Wildlife in Canada.
  • COSEWIC Annual Report 2019 to 2020 (2020-09-02)

    Over the past year COSEWIC assessed a total of 21 wildlife species, none of which were assigned a status of Not at Risk. Of these 21, COSEWIC re-examined the status of nine wildlife species; of these, 44% were reassessed at the same or lower level of risk. To date and with the submission of this report, COSEWIC’s assessments now include 810 wildlife species in various risk categories including 363 Endangered, 190 Threatened, 235 Special Concern, and 22 Extirpated (i.e. no longer found in the wild in Canada). In addition, 19 wildlife species have been assessed as Extinct, 59 wildlife species have been designated as Data Deficient, and 198 have been assessed as Not at Risk.

Consultation Documents

  • Consultation on Amending the List of Species under the Species at Risk Act - Terrestrial Species (2008-03-10)

    As part of its strategy for protecting wildlife species at risk, the Government of Canada proclaimed the Species at Risk Act (SARA) on June 5, 2003. Attached to the Act is Schedule 1, the list of the species that receive protection under SARA, also called the List of Wildlife Species at Risk. Please submit your comments by March 25, 2008 for species undergoing normal consultations and by March 27, 2009 for species undergoing extended consultations.
  • Consultation on Amending the List of Species under the Species at Risk Act: Terrestrial Species December 2020 (2020-12-02)

    COVID-19 and the consultations on the listing of species at risk As a result of the ongoing COVID 19 situation, it is not possible to have in-person meetings. Taking this into consideration, please note that consultation closing dates have been set for both the Normal and Extended consultations for the terrestrial species considered in this document. We will work to ensure that all the known, potentially affected parties have the opportunity to contribute to the consultations and that the consultation process is flexible and sensitive to the current context. If you wish to contribute, please submit your comments by April 2, 2021 for species undergoing normal consultations and by September 2, 2021 for species undergoing extended consultations. You may provide comments by email, letters, or through the online survey. The Government of Canada is committed to preventing the disappearance of wildlife species at risk from our lands. As part of its strategy for realizing that commitment, on June 5, 2003, the Government of Canada proclaimed the Species at Risk Act (SARA). Attached to the Act is Schedule 1, the list of the species provided for under SARA, also called the List of Wildlife Species at Risk. Extirpated, Endangered and Threatened species on Schedule 1 benefit from the protection afforded by the prohibitions and from recovery planning requirements under SARA. Special Concern species benefit from its management planning requirements. Schedule 1 has grown from the original 233 to 622 wildlife species at risk. Please submit your comments by April 2, 2021, for terrestrial species undergoing normal consultations and by September 2, 2021, for terrestrial species undergoing extended consultations. For a description of the consultation paths these species will undergo, please visit the Species at Risk (SAR) Public Registry website at: The Minister of the Environment's Response to Species at Risk Assessments. To respond to survey questions, please go to the survey page. Consultation ends on April 2, 2021 for species undergoing a normal consultation process and on September 2, 2021 for species undergoing an extended consultation process.

Recovery Document Posting Plans

  • Environment and Climate Change Canada's Three-Year Recovery Document Posting Plan (2016-07-06)

    Environment and Climate Change Canada’s Three-Year Recovery Document Posting Plan identifies the species for which recovery documents will be posted each fiscal year starting in 2014-2015. Posting this three year plan on the Species at Risk Public Registry is intended to provide transparency to partners, stakeholders, and the public about Environment and Climate Change Canada’s plan to develop and post these proposed recovery strategies and management plans. However, both the number of documents and the particular species that are posted in a given year may change slightly due to a variety of circumstances. Last update December 2, 2021
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