The few studies of the activities and home ranges of wild least weasels have all been done by snow tracking. For example, over a 13-day period from December
20, 1939, Polderboer (1942) recorded weasel tracks on his farm in Iowa. He found the trails and resting sites of what appeared to be four least weasels, and calculated that each occupied an area of less than 1 ha. The weasels lived in the fencerows and slept in nests of grass and corn husks, originally made by mice, entered through burrows of 2.5 cm in diameter or less.
Polderboer confirmed the identity of the animals making the tracks by trapping each one at a den in a steel trap. None of the dens was lined with fur or had a latrine nearby, which suggests that the weasels were not long-term residents and that their real home ranges were undoubtedly larger than 1 ha. Nevertheless, this figure entered the literature at a time when little else was known about the ecology of least weasels, and when plugged uncritically into calculations of the extent of predation pressure exerted by an average population density of least weasels, produced comic results (Chapter 7). A later estimate of the ranges of least weasels on winter-ploughed fields was 4 to 10 ha (Polder 1968) (Table 8.1). Their dens were concealed under the furrows, and they pursued mice and voles through the small spaces between the turf or stubble sods.
In Finland in the winters of 1952-1958, Nyholm (1959a) systematically observed the tracks left by least weasels in snow-covered fields and copses, and along the banks of rivers and lakes. He reckoned that least weasels ranged over less than 3 ha, although he remarked that it was difficult to determine the ranges exactly because the weasels moved about so much under the snow. Naturally, much depends on how hard it is to find food. In the Kola Peninsula, in the far north of European USSR, voles and least weasels were numerous in the summer of 1938. The voles crashed to very low numbers in the following autumn, and least weasels tracked during the winter of 1938-1939 were hunting over extended home ranges of up to 10 ha (Nasimovich 1949).
Klemola et al. (1999) tracked least weasels and stoats during winter in Finland for 6 years through the 1980s. At the same time, they monitored the abundances of field, sibling, and bank voles. As expected, least weasels traveled farther (males 1,395 m, females 1,015 m per trip) when voles were scarce than when they were abundant (660 m, 110 m, respectively). Weasels also traveled farther in farmland than in forested areas, but exactly what this means is not clear. One possible explanation is that weasels actively preferred to forage for rodents in farmland, but an alternative is that the researchers could more easily find and follow their tracks in open country than under trees.
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