Northern Prairie Wildlife Research Center
Habitat and History. The geographic range of the ermine in the prairie pothole region is restricted primarily to the aspen parkland, whereas the range of the long-tailed weasel includes all of the region (Soper 1946; Rand 1948b; Banfield 1974; Simms 1979; Gamble 1981; Hall 1981). The long-tailed weasel is adapted to the prairie (Bailey 1926; Soper 1961; Jones et al. 1983). Population trends of the ermine and long-tailed weasel in the region are largely unknown, but seemingly both species were common during presettlement times (Bailey 1926; N. Criddle 1929). The extensive conversion of grasslands, wetlands, and woodlands to cropland must have reduced the abundance of weasels. The decline in harvest of long-tailed weasels in Saskatchewan from >60,000 pelts annually in the 1930's to <1,500 annually in recent years has been attributed largely to habitat changes (Fagerstone 1987).
Populations of weasels, especially ermines, fluctuate greatly in response to availability of food, especially small mammals (Gamble 1981). Population buildups of weasels occur periodically in the prairie pothole region and, because weasels are bold and curious mammals, such buildups should be evidenced by increased sightings.
Population Structure. Adult male weasels seem to be intolerant of each other, except during kit-rearing (Jones et al. 1983), and occupy territories in which one or more females may reside (Ewer 1973; Fagerstone 1987). Home ranges of ermines and long-tailed weasels range from a few hectares to >1 km2, depending on habitat type and food abundance; males occupy larger areas than females (Fagerstone 1987). Estimates of weasel densities in the prairie pothole region were not found, but estimates elsewhere range from about 4 to 6/km2 for ermines and <1 to 38/km2 for long-tailed weasels (Fagerstone 1987).
Distribution and Abundance. All seen weasels were recorded as long-tailed weasels, but some were probably ermines, especially in the aspen parkland. Weasels were seen in 11 (69%) of the 16 study areas in Canada and in 9 (53%) of the 17 study areas in the United States (Fig. 12); sightings were infrequent in all areas (Appendix Table 10). Data were inadequate to rate abundance of weasels in individual areas. The maximum number of different annual sightings of weasels in study areas in Canada was four in one area (Hay Lakes) in 1983 and in the United States, seven in one area (Fredonia) in 1987. The abundance of meadow voles was noticeably high (seen daily during conduct of field work) in both of those study areas during those study years. Ten of 11 weasels caught during removal of predators from three small unit management study areas were from one area (Fredonia; Appendix Table 3).
Available information indicates weasels were rather uniformly distributed throughout the prairie pothole region and populations were low.
Fig. 12. Study areas in the prairie pothole region in which weasels (ermine and long-tailed weasels) were seen during annual surveys in the 1-3 years each area was studied, 1983-1988 (Appendix Table 10).