Ecology of the stoat in Nothofagus forest: Home range, habitat use and diet at different stages of the beech mast cycle

We studied the ecology of a high-density population of stoats in Fiordland, New Zealand, in the summer and autumn of 1990-91 following a Nothofagus seeding in 1990. Results are compared with findings from the same area in 1991-92, a period of lower stoat density. In the high-density year, minimum home ranges (revealed by radio-tracking) of four females averaged 69 ha and those of three males 93 ha; range lengths averaged 1.3 km and 2.5 km respectively. Neither difference was statistically significant. For combined sexes, average range area in the high-density year was significantly less, and range length was significantly shorter, than in the following year. When we compared stoat diet in the high-density year with that in the following two years, there were no significant differences in the frequencies of occurrence of birds or invertebrates in stoat guts. Overall, bird remains were found in 56% of guts, and invertebrates in 28%. Possum remains occurred in 6% of male stoats but were never found in females. Mice were only detected in stoats in the high-density year, when they occurred in 54% of guts. Lagomorphs occurred significantly more often in the guts of stoats during lower-density years (26%) than the high- density year (7%). Seedfall in Nothofagus forest is synchronous and periodic. Following seedfall, mouse density rises dramatically, followed by a sharp rise in stoat numbers. It has been suggested that mice feed on the abundant seed and that stoats in turn increase because of the large numbers of mice available to them. We suggest that the situation is more complex and that increases in not only mouse, but also bird (and possibly invertebrate), densities may contribute to the high productivity of stoats in the year following a Nothofagus seedfall.