Distribution and Abundance of Predators that Affect
Duck Production: Prairie Pothole Region
Species Accounts -- Carnivores
Mink
Habitat and History. The prairie pothole region is in the center of the geographic range of the mink in North America (Hall 1981). Unlike the other studied carnivores, populations of this predator may not have been affected greatly by settlement (Bird 1961). Although minks are distributed throughout the region, they are not common everywhere or every year (Bailey 1926; Soper 1946, 1961). Minks depend on aquatic habitat. Rivers, streams, freshwater lakes, and deep marshes that contain prey such as fishes, crayfishes, and muskrats (Ondatra zibethicus) are preferred (Bailey 1926; Eagle and Whitman 1987). Minks also inhabit shallow prairie wetlands where their diet includes meadow voles (Microtus pennsylvanicus), waterbirds, aquatic insects, and tiger salamander (Ambystoma tigrinum) larvae (Eberhardt and Sargeant 1977; Arnold and Fritzell 1987b).
Minks that inhabit shallow prairie wetlands lead a precarious existence because annual fluctuations in water level affect abundance of food and availability of shelter. Frequent widespread and local droughts characteristic of the region lower reproductive performance by minks (Eberhardt 1974) and availability of prey. Shallow wetlands often freeze to the bottom during winter. The widespread severe droughts of the 1910's, 1930's, 1960's, and 1980's (Stoudt 1971; Kiel et al. 1972; Reynolds 1987) probably had catastrophic effects on the abundance of minks in the region.
Population Structure. Mink populations in spring are composed of territorial males that occupy large areas and females that occupy small areas (Gerell 1970; Whitman 1981; Eagle and Whitman 1987; Eagle 1989). Nearly all studies of spacing and movements in minks have been in riverine, lacustrine, and coastal habitats where home ranges are best measured in terms of lengths of waterways or lengths of used shorelines rather than size of used areas. In prairie pothole habitat, minks tend to occupy circular home ranges that may encompass many wetlands. Arnold (1986) reported that home ranges of adult male minks during May through July in pothole habitat of Manitoba (near the Moore Park study area) averaged 6.5 km2 (range = 3.2-16.3 km2) and included an average of all or parts of 285 wetlands. Female minks rearing kits seem to restrict their activities in spring to one or few wetlands (Eberhardt and Sargeant 1977; Eagle 1989).
Distribution and Abundance. Minks were detected in only three study areas in Canada but were present in all nine small unit management study areas in the United States (Fig. 11). (No data on mink tracks were available from the eight Central Flyway study areas.) The percentage of study areas where minks were common or more abundant was greater in the United Stated than in Canada (Appendix Table 6). Mink tracks were found in all nine small unit management study areas each study area-year except in one (Eldridge) in 1987 (Appendix Table 5). In addition, minks were seen in all those study areas except one (Eldridge) during one or more study years (Appendix Table 10).
Although minks were not numerous in any study area, they were common in the three study areas in Minnesota and in two (Kulm and Litchville) in North Dakota. They were most common in the three study areas in Minnesota where their tracks were found in 43-67% of quarter sections searched each year and about twice as abundant as in any other area (Appendix Table 5). The relatively high abundance of minks in the study areas in Minnesota reflected favorable habitat that included numerous permanent wetlands and streams in and near each area.
The higher mink populations in small unit management study areas in North Dakota than in study areas in Canada (Fig. 11) probably reflected locations of study areas in the more temperate part of the prairie pothole region and selection of study areas. Although no data on mink tracks were collected in the Central Flyway study areas, no minks were observed in those areas during 3,468 observation-hours (Appendix Table 10), indicating low populations. Drought prevailed when those areas were studied. A criterion for choosing the small unit management study areas was that each should have many and diverse wetlands. One study area (Eldridge) with no mink sightings (Appendix Table 10) and the lowest mink track index of any small unit management study area (Appendix Table 5) had the fewest semipermanent wetlands of any such area.
In Canada, mink tracks were found in three study areas (Ceylon, Craik, Moore Park; Fig.11). In each of those areas, the tracks were in only 1 or 2 adjoining quarter sections, indicating presence of a single mink; abundance in each area was scarce. No minks were seen in any study area in Canada during 23,954 observation-hours by field personnel (Appendix Table 10). Although minks were more difficult to detect than larger carnivores, we are confident that the data from Canada accurately portrayed populations in study areas as very low or absent. Many excellent sites for mink tracks were examined in each area. The drought and absence of rivers, continuously flowing streams, and permanent wetlands in most study areas probably contributed to the low mink populations.
Fig. 11. Percentage of searched quarter sections (in black) by study area in which mink tracks were found or in which the abundance of tracks was estimated during two systematic annual searches in April-June in >= 1 study year and ratings of the abundance of minks in each area, 1983-88. Results for study areas searched >1 year were averaged; study areas are in the prairie pothole region.
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