The first live-trapping study of the home ranges and social organization of weasels has become a classic and is often cited. It was done in the Carron Valley, near Stirling in Scotland, by Lockie (1966), in a young pine plantation overgrown with thick grass full of field voles. On his 32-ha study area (surrounded by about 800 ha of similar plantations), Lockie found 10 male common weasels, each jealously guarding a plot of1 to 5 ha (Table 8.1; Figure 8.3). Transient males (at least 20) passed through all year round, especially in late summer and again in early spring. These were usually caught only once. Occasionally one would settle for a while, but its movements were much restricted, often to only one trap. The three known resident females lived on much smaller areas and each was caught repeatedly in only one trap. Unlike the males, they had no contact with each other. Six transient females were caught once each.
When Lockie began his study in November 1960, the weasels' territories were already established. They remained stable until November 1961. Then, for reasons that have never been explained, and at a time when weasels are normally settling into steady home ranges for the winter, the system broke down even though the voles were still very abundant (almost 300 per ha). Some residents died, others disappeared, and those that were left seemed to lose contact with each other. Over the next 2 years, to the end of 1963, enough common weasels entered the area to populate it, as it had been in 1961, 10 times over, but never more than two lived there at one time, and the system of contiguous, defended territories was never reestablished. By May 1962, the numbers of field voles were down to 44 per ha.
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