Population-Structure and Dispersal of Peak-Year Cohorts of Stoats (Mustela erminea) in 2 New Zealand Forests, with Special Reference to Control

During a peak summer for stoats in 1979/80 (density indices in two study areas 8.2 and 10.7 new captures per 100 trapnights) a total of 134 stoats were caught, marked and released (86% young of the year, 58% males). Fifty-seven of 110 stoats were recaptured at least once, of which 42 moved 0.4–1.6 km between first and second captures. Frequency distri- butions of numbers of captures and first recapture-distances up to 1.6 km were similar in males and females, adults and young, but Leslie's test showed significant (P<0.05) inequality of catchability of 21 stoats known to be present over seven trapping rounds. Dispersal movements recorded by young males exceeded 20 km. Nine males and five females, from a possible 107 animals, were recovered up to 18 months after the end of livetrapping. Significantly more marked adult males (45%) than young males (9%) were recovered. Two important implications of these data for conservation are (a) kill-trapping over large areas at considerable effort (400 m trap spacing) may only hasten an inevitable post-peak decline in stoat density, because the chances of capture are low and not the same for all stoats; and (b) those killed may be replaced by immigrants from over 20 km away.