Rodents

There are twenty-seven native rodent species in Saskatchewan (see Table RO-1 on the following page). At least two more species (the long-tailed vole, Microtus ochrogaster , and the Western harvest mouse, Reithrodontomys megalotis) may occur naturally because they are found nearby. Additional species associated with European settlement are the Eastern fox squirrel (Sciurus niger) and Eastern gray squirrel (Sciurus carolinensis) of eastern North America, and the European house mouse (Mus musculus), the Norway rat (Rattus norvegicus), and occasionally the black rat (Rattus rattus). The squirrels occur widely in urban areas of southern Saskatchewan. The rats are commensal species in buildings and garbage dumps. Efforts at eliminating rats from many parts of the province have been successful. House mice are found mostly at building sites, but small numbers are found in the wild in the south.

Beavers are the largest Saskatchewan rodents; exceptional individuals exceed 39 kg and 1.2 m in length. The 12 g olive-backed pocket mouse is the smallest species. The shortest rodents in the province are the extremely short-tailed 120 mm sagebrush voles. The most common rodent in the province is the meadow vole; deer mice, although more abundant in the southwest, are rarely seen. The semi-aquatic beavers and muskrats have dense fur that traps an insulating layer of air that prevents the skin of the animals from contacting water. These pelts are highly desirable, and European exploration and early economic development of Saskatchewan were largely driven by the search for and the marketing of beaver pelts. Beavers remain the dominant fur-producing species: the 28,299 pelts sold in 2001–02 from the province were 32% of the total fur take, representing $688,000 (approximately 35%) of the value of furs produced in that year. Over-trapping virtually extirpated the species by the early 1900s. However, due to reintroduction, the animals are now found in virtually all suitable habitats across the province.

Beavers are known for their large flattened tail that is slapped on the water as a warning and serves as a site for storage of fat. The animals dam small streams; the impounded water is used for protection as well as transport and cache of branches and sections of tree trunks, from which the bark is eaten for winter food. The animals make well-defined trails and often canals that lead from the pond to treed areas. In ponds, the animals build large lodges with an entrance under the water. On rivers, beavers burrow deeply into the banks to make shelters. Beaver ponds provide habitat for waterfowl, frogs, and other aquatic organisms. Flooding often drowns trees that remain standing, providing habitat for swallows and other cavity-nesting birds. Over long periods, beaver dams gradually fill in with vegetation that, in northern areas, can eventually convert a small stream into a series of bogs.

The second-largest Saskatchewan rodent is the porcupine, which occurs throughout the province, including the sparsely treed plains. The animals eat a variety of vegetable foods during the summer, and subsist on the cambium layer of bark and sometimes needles of conifers during the winter. Pressed by a threat, they instinctively crouch and raise their quills. This is a habit that, while effective against most predators, accounts for the many porcupines run over on roadways. Porcupines cannot throw their quills, but loose ones can fly off when the animal attempts to slap the attacker with its heavily quilled tail. Once imbedded, the barbed quills work their way into the flesh; cutting the ends of the hollow quills may cause them to relax and make them easier to pull out. Porcupines mate in the manner of other mammals, with the female flattening her quills.

Burrowing by rodents such as ground squirrels and northern pocket gophers turns over the soil. Soil mounds are locations for the establishment of new plants. Northern pocket gophers can become numerous in alfalfa plantings and gardens, and do considerable damage by eating the roots. The animals’ mounds can make the ground rough, making haying difficult and occasionally resulting in damaged machinery. In addition to using their powerful front limbs, pocket gophers dig with their teeth. They also burrow under the snow and fill the snow tunnels with dirt from burrowing; when the snow melts in the spring, a pattern of dirt casts is left. They regularly forage above ground during the night, and are a frequent prey of the great horned owl. Northern pocket gophers are sometimes called “moles” because of the mounds of earth they push to the surface; but moles are insectivorous animals whereas pocket gophers are vegetarian. “Pocket” applies to the external cheek pouches that are used for transporting food. While “gopher” is often used for ground squirrels, “ground squirrel” is preferred to avoid confusion with pocket gophers.

Richardson ground squirrels prefer grasslands with sparse vegetation, and often increase in numbers when grazing reduces vegetation. Control measures are most effective before the young are born in late April and early May, and before the females start to enter hibernation in August. Unlike Franklin’s ground squirrels (“bush gophers”), which are frequently encountered in the parklands, and also the distinctive thirteen-lined ground squirrel (“striped gopher”), Richardson’s ground squirrels do not have to drink water to survive.

Rodents are implicated in the spread of disease. Hanta virus can cause serious infection in humans. The virus is highly contagious among deer mice and other small rodents, but it does not cause severe illness. Spread of the virus to humans is usually through dust from dried droppings or urine. Wearing dust masks and rubber gloves when cleaning up mouse nests or dusty areas frequented by mice, such as granaries, is recommended. Sylvatic plague, while rare, can be contracted during handling of Richardson’s ground squirrels and prairie dogs.

Numbers of small rodents vary dramatically. In forested areas, meadow voles undergo a 3–5 year cycle. On the plains, where weather is less predictable, very large numbers of meadow voles and deer mice occur when favourable conditions prevail. Meadow voles are particularly likely to increase because of the short 3–4 week generation time and ability to breed year-round, especially if food such as unharvested crops is available under heavy snow cover. Many rodents hibernate in winter. Northern populations of black-tailed prairie dog undergo true hibernation, whereas more southern populations do not. Other hibernators include meadow and Western jumping mice, woodchucks, all the ground squirrels, and probably olive-backed pocket mice.

Tim Schowalter

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Further Reading

Baker, R.J., et al. 2003. Revised Checklist of North American Mammals North of Mexico. Museum of Texas Technical University Occasional Papers, Number 229; Banfield, A.W.F. 1974. The Mammals of Canada. Toronto: University of Toronto Press; 2001. Natural Neighbours: Selected Mammals of Saskatchewan. Regina: Canadian Plains Research Center.