A comparison of population estimates and abundance indices for house mice inhabiting beech forests in New Zealand

Abstract

Populations of house mice were sampled on nine grids in Fiordland National Park between May and November 1999, using live-capture and footprint-tracking tunnel methods. Trapped mice were removed from three grids (approximately 3.24 ha each), and marked and released on the other six. Density estimates were obtained using recapture data from the grids where mice were released (M_h (jackknife) model from program CAPTURE), and rate-of-capture data from grids where mice were removed (M_bh (removal) CAPTURE model). Density estimates were used to evaluate the performance of 4 indices of mouse abundance by contrasting R²-values of their regression on estimated mouse density. Indices evaluated were: minimum number of individuals known to be alive (MNA) (total number of individual mice caught over the course of a trapping session), one-night trap catch (number of mice caught on first night of each trapping session expressed as captures per 100 trap-nights), three-night trap catch (same index estimated from number of mice caught over the first three nights), and tracking-tunnel index (proportion of nine tunnels that had mouse tracks). While MNA, one-night trap catch, and three-night trap catch were all significantly correlated with estimated density, MNA was most strongly correlated, with R² varying between 0.67 to 0.87 depending on whether 3, 4 or 5 nights’ capture data were used. Variation in tracking-tunnel index was unrelated to mouse density on our grids.