Species Profile

Western Harvest Mouse dychei subspecies

Scientific Name: Reithrodontomys megalotis dychei
Other/Previous Names: Western Harvest Mouse (Prairie population)
Taxonomy Group: Mammals
COSEWIC Range: Alberta
COSEWIC Assessment Date and Status Change: November 2019
COSEWIC Status: Endangered
COSEWIC Status Criteria: B1b(v)c(iv)+2b(v)c(iv)
COSEWIC Reason for Designation: This tiny mouse occurs at the northern edge of its distribution at the Suffield National Wildlife Area in southeastern Alberta, and is one of two designatable units of the species in Canada. It is among Canada’s shortest-lived mammals. Populations monitored in the United States suggest extreme fluctuations in the number of mature individuals. These fluctuations increase the vulnerability of the species to disturbances, when numbers are low in spring and early summer. Although comprehensive data describing population abundance and trends are lacking, existing capture data suggest a decline in the number of mature individuals since 2011. That decline in the species’ small range and extreme fluctuations in abundance are the reasons for designation. Climate change, including the possibility of more frequent wildfires and intense drought, is an increasing future threat.
COSEWIC History of Status Designation: Species considered in April 1994 and placed in the Data Deficient category. Re-examined in April 2007 and designated Endangered. Status re-examined and confirmed in November 2019.
SARA Status: Schedule 1, Endangered
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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Quick Links: | Photo | Description | Habitat | Biology | Threats | Protection | Recovery Initiatives | National Recovery Program | Documents

Image of Western Harvest Mouse dychei subspecies

Western Harvest Mouse dychei 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 total length, half of which is its tail. This tawny mouse has a dark dorsal stripe that runs from the forehead to the tail. It has white hind feet, buff sides and cheeks, and white to deep grey fur on its undersides. It has a long, sparsely furred tail that is grey above and mostly white below and prominent naked ears. The Western Harvest Mouse may be confused with the larger, more common deer mouse and house mouse. However, juvenile deer mice are most often grey in colour, and house mice have completely naked tails.

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Distribution and Population

The Western Harvest Mouse is found throughout much of west-central Mexico and the western United States. To the north, it is found in western Canada, where it is restricted to the grasslands of south-central British Columbia and southeastern Alberta. The subspecies dychei and megalotis are found in Alberta and British Columbia, respectively.   In Alberta, the Western Harvest Mouse has been observed at only four localities. Prior to 1994, its distribution was based on three museum specimens collected near Milk River, Medicine Hat, and in the Pinhorn Grazing Reserve near Manyberries. During 1994 and 1995, 95 Western Harvest Mice were captured within the Canadian Forces Base Suffield National Wildlife Area, a location separated from the other three. With the exception of the Suffield records, the species has not been documented in Alberta since 1966. Furthermore, despite substantial sampling, no Western Harvest Mice have been found in owl pellets in Suffield or other areas in southeastern Alberta. The analysis of owl pellets is an excellent means of sampling for these mice. These data suggest that Western Harvest Mice are extremely rare in Alberta.   There are no data available on population size or trends at either the provincial or national level.

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Habitat

Little is known about the detailed habitat requirements of the Western Harvest Mouse, but it has been found in habitats with dense vegetation cover consisting of tall grasses or shrubs, such as antelope bitterbrush or sagebrush.   In Alberta, the species is believed to be associated with flat or gently undulating grasslands with sandy soils. It seems to occur in several types of habitats, including dry gullies that border grasslands, old fields, and ponderosa pine forests.

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Biology

In the Canadian populations, the breeding season runs from late spring to late summer. Females can breed at the age of four months and may have up to five litters per season, with an average of three young per litter. Western Harvest Mice build small grass nests on the ground or up to 1 m above the ground in shrubs. They do not dig burrows, but they sometimes use the burrows of other small mammals. Western Harvest Mice appear to be able to enter torpor to cope with cold temperatures. This dormant state, in which vital functions are slowed down, may be essential to the survival of the Canadian populations. Some researchers speculate that they hibernate, although this may not occur within southern British Columbia as this species has been observed throughout the year. This nocturnal mouse eats mainly seeds and insects such as caterpillars and moths. It also eats new plant growth and flowers. In Canada, owls are the only confirmed predators of Western Harvest Mice, but other possible predators include prairie rattlesnakes, hawks, jays, shrikes, raccoons, foxes, weasels, skunks, badgers, and coyotes. Although Western Harvest Mice can live for 18 months in the wild, few individual mice live past 6 months.

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Threats

Western Harvest Mice are susceptible to habitat change resulting from fire, such as the disappearance of vegetation cover and food, but populations can recover quickly provided there is suitable unburnt habitat nearby.   Habitat fragmentation and loss caused by urban development, grazing, mowing, and agriculture are likely the most significant threats to the Alberta population.

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Protection

Federal Protection

The Western Harvest Mouse dychei 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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Recovery Initiatives

Status of Recovery Planning

Recovery Strategies :

Name Recovery Strategy for the Western Harvest Mouse (Reithrodontomys megalotis dychei) in Canada
Status Final posting on SAR registry

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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.

16 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 dychei subspecies (2007-12-04)

    This subspecies has a limited range and has been found at only one location in the past 40 years; this location is isolated from others. Dispersal distance is limited and the population fluctuates. This species is commonly found in owl pellets in the USA, but none have been reported in owl pellets (including burrowing owls) in Suffield or other areas in southeast Alberta, despite substantial sampling. Owl pellet analysis is an excellent means of sampling for these mice.
  • Response Statement - Western Harvest Mouse dychei subspecies (2020-12-02)

    This tiny mouse occurs at the northern edge of its distribution at the Suffield National Wildlife Area in southeastern Alberta, and is one of two designatable units of the species in Canada. It is among Canada’s shortest-lived mammals. Populations monitored in the United States suggest extreme fluctuations in the number of mature individuals. These fluctuations increase the vulnerability of the species to disturbances, when numbers are low in spring and early summer. Although comprehensive data describing population abundance and trends are lacking, existing capture data suggest a decline in the number of mature individuals since 2011. That decline in the species’ small range and extreme fluctuations in abundance are the reasons for designation. Climate change, including the possibility of more frequent wildfires and intense drought, is an increasing future threat.

Recovery Strategies

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.

Permits and Related Agreements

  • Explanation for issuing permit(#SARA-PNR-2009-0116), persuant to the provisions of section 73 of SARA (2009-08-27)

    The purpose of this study is to determine the distrubution and abundance of the Western Harvest Mouse on the Suffield National Wildlife Area. Mice will be sampled using live trapping. Traps will be set at 20 locations with an emphasis on historically occupied locations. At each site a trapping network of 57 traps will be deployed. Traps will be set at dusk and checked at dawn each day. Traps will be camouflaged by covering them with nearby vegetation for insulation and concealment. Traps will be closed after checking each morning to prevent capture of animals during the heat of the day. Traps will be placed within the preferred habitat areas of wet meadow and dense shrubby grassland to the extent possible. Captured individuals will be placed into handling bags and led into mesh inspection tubes for species determination, hair clipping and hair collection. Captured individuals will be marked using temporary methods such as hair clipping or marking with surgical ink to uniquely identify them. A small sample of hair, approximately 10 hair roots, will be extracted from each captured individual for DNA analysis. Photographs of diagnostic identification features will be taken. Average handling time is expected to be less than 2 minutes per specimen.
  • Explanation for issuing permit(#SARA-PNR-2010-0153), persuant to the provisions of section 73 of SARA (2010-08-09)

    The purpose of this study is to determine the distribution and abundance of the Western Harvest Mouse on the Suffield National Wildlife Area. Mice will be sampled using live trapping. Traps will be set at 80 locations with an emphasis on historically occupied locations. At each site a trapping network of 57 traps will be deployed. Traps will be set at dusk and checked at dawn each day. Traps will be camouflaged by covering them with nearby vegetation for insulation and concealment. Traps will be closed after checking each morning to prevent capture of animals during the heat of the day. Traps will be placed within the preferred habitat areas of wet meadow and dense shrubby grassland to the extent possible. Captured individuals will be placed into handling bags and led into mesh inspection tubes for species determination, hair clipping and hair collection. Captured individuals will be marked using temporary methods such as hair clipping or marking with surgical ink to uniquely identify them. A small sample of hair, approximately 10 hair roots, will be extracted from each captured individual for DNA analysis. Photographs of diagnostic identification features will be taken. Average handling time is expected to be less than 2 minutes per specimen. Fluorescent tracing powder will be applied to the belly and feet of 20 animals.
  • Explanation for issuing permit(#SARA-PNR-2011-0178), persuant to the provisions of section 73 of SARA (2011-06-16)

    This is a continuation of the previous year's study due to the limited results obtained. The specific purpose of this study is to determine the abundance, distribution, and habitat use of the western harvest mouse (Reithrodontomys megalotis dychei) at Suffield National Wildlife Area (NWA) for the purposes of identifying critical habitat. Mice will be sampled using live traps. Traps will be set at up to 80 locations across the NWA within a variety of habitat types. At each site a network of approximately 57 baited traps will be deployed. Traps will be set at dusk and checked at dawn each day. Captured mice will be placed into bags and led into mesh tubes to identify the species and enable hair removal for DNA analysis and marking. Approximately 10 to 20 hairs will be collected for DNA analysis. Individuals will be marked using inert die (surgical ink). Fluorescent tracing powder will be applied to the belly and feet in order to follow the movements of the mice. Up to 100 mice will be trapped per year. Up to 10 individuals per year will be fitted with 0.55 g radio transmitters to follow movement and habitat use. Transmitters will be left on the mice for two weeks. This species is regulated under the Species at Risk Act. This location is a federal land.

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.

Critical Habitat Descriptions in the Canada Gazette

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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