Wlodek Jgdrzejwski and Bogumila Jgdrzejwska began to work on carnivores in the Bialowieza Forest in Poland in the 1970s, and in the mid-1980s they extended their work to the entire community of vertebrate predators and prey (Jgdrzejwska & Jgdrzejewski 1998). Bialowieza Forest is an exceptional example of European temperate deciduous and mixed forest, and a third of its area remains in old growth forest of natural origin that has never been logged. The Forest is large, spatially integrated with other extensive forest tracts in Poland and Belarus, and sparsely populated by people (two to three people per km2). Jgdrzejwska and Jgdrzejwski snowtracked common weasels each winter starting in 1985, and radio tracked 12 weasels in 1990-1991. Bank voles and yellow-necked mice were common in the forest, and root voles were common in marshlands. Densities of rodents were generally moderate (25 to 75 rodents per ha) but irrupted following the synchronous seeding of oaks, hornbeams, and maples, peaking in 1990 at more than 300 rodents per ha and then crashing.

The weasels were active predominantly during daylight, with a peak around noon (Jgdrzejwski et al. 2000). On average they left their nests for a total of just under 4 hours per day, depending on the season. In winter, weasels went out once or twice each day for 1 to 2 hours at a time, while in summer they usually went out three to four times, and some days as many as seven times. They were, as one might expect, most active during the mating season.

When rodents were abundant on the forest floor, the ranges of five radio tracked male common weasels ranged from 11 to 37 ha, but after the rodents disappeared, the two different males radio tracked after the crash in rodent densities covered 117 and 216 ha (Jgdrzejwski et al. 1995; Jgdrzejwska & Jgdrzejewski 1998). These are amazing areas for a small, short-legged animal to cover, but snow tracking confirmed them. During the peak, a rough estimate of weasels' ranges could be obtained from plotting tracks along transects through the Forest and making some limited assumptions about distances between tracks of different weasels. The assumptions were tested as far as possible with the telemetry data. Snow tracking yielded an average home range diameter (both sexes) of about 400 m, making a circular area of 13 ha during the rodent peak, and an average diameter of 1000 m, or 75 ha, after the crash. As predicted by theory (Powell 1987, 1989, 1994), when rodents were extremely abundant, male weasels tolerated extensive overlap of home ranges and shared their ground with transients.

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