The elusive western harvest mouse (Reithrodontomys megalotis) is one many species in the Thompson Watershed. Weighing approximately 11 grams and measuring an average of 136 mm in total length, the western harvest mouse is a small, brownish rodent with a faint dark dorsal stripe running the length of its body from head to tail. Its size and coloration help it blend into the grasslands and shrub-steppe environments of the region. This small rodent, often overlooked due to its diminutive size and nocturnal habits, plays a significant role in the ecological fabric of the area.

Habitat

The western harvest mouse is known for its preference for habitats characterized by tall herbaceous cover. In the Thompson Watershed, this species is found in valley bottoms or south-facing slopes, thriving in shrub-steppe grasslands with abundant tall grasses such as bluebunch wheatgrass and shrubs like sagebrush. These habitats provide the necessary cover and food resources for the mouse to flourish.

Little is known about the detailed habitat requirements of the western harvest mouse, and much of the information about habitat preference has been inferred from the types of habitats where the mouse is most often captured. Ongoing research and monitoring are crucial to gain a better understanding of this species’ needs and to inform conservation strategies.

Threats

Loss of Habitat

The most significant threat to the western harvest mouse in the Thompson Watershed is the urban and agricultural development that leads to habitat loss. The expansion of cities and the conversion of natural landscapes into farmland can permanently alter the habitats that these mice rely on for food, shelter, and breeding. Livestock grazing can also degrade the quality of the grassland habitats that are essential for the mouse’s survival, leading to a reduction in suitable living areas.

Predation by Cats

Cats, both those that are pets and those that live in the wild, have a natural hunting instinct that can lead to the predation of small mammals like the western harvest mouse. The impact of cat predation on the western harvest mouse population is a concern, as it can contribute to the decline of this species, especially where cats are abundant or where the mouse’s habitat overlaps with urban areas.

Rodenticides

While rodenticides may impact local populations of the western harvest mouse, the overall impact from rodenticide poisoning is currently thought to be low due to the limited use of these chemicals within the species’ range. However, it is essential to monitor the situation closely, as changes in land use or pest management practices could alter this assessment.

Conservation Efforts

While some areas of western harvest mouse habitat in British Columbia are protected within provincial parks and ecological reserves, there are ongoing discussions to create more grassland parks in the Okanagan and Similkameen valleys. The mouse is protected under the British Columbia Wildlife Act, reflecting the importance of conserving this species and its habitat.

According to the Government of Canada’s Management Plan for the Western Harvest Mouse, the western harvest mouse is a species of Special Concern because it has a limited range and small extent of occurrence and area of occupancy. The management goal to protect these creatures is to maintain stable or increasing populations of the western harvest mouse distributed throughout the species’ known range in BC.

Photo: Western Harvest Mouse by lynch820 via iNatuaralist, CC-BY-NC

Additional Resources

• E-Fauna BC
• Government of Canada
• Nature Serve Explorer