Improving predator capture rates: analysis of river margin trap site data in the Waitaki Basin, New Zealand

We recorded trap site characteristics and captures during a trapping programme designed to protect breeding and released black stilts (kaki, Himantopus novaezelandiae) from predation, in order to learn about trap site features that might improve the efficacy of future predator trapping management. Captures were made at 1629 leg-hold traps opened over 71 333 trap nights between 1998 and 2000, at six locations in the Upper Waitaki Basin, New Zealand. Twelve trap site variables were recorded. The model describing the best combination of variables for four groups of predators (cats Felis catus, mustelids Mustela furo (ferrets) and M. erminea (stoats), harriers Circus approximans and hedgehogs Erinaceus europaeus) was found using logistic regression and AIC values. For all predator groups both the way the trap was set and its placement within the landscape (with respect to habitat type and the distribution of landscape features that might be important to predators) influenced capture rates. Mustelids and harriers were more likely to be caught on stable riverbed habitats where rabbit densities are highest, while hedgehogs were mainly caught on river terraces and cats were equally likely to be caught anywhere. Individual trap characteristics in terms of set type, trap haze, trap backing, plate haze, visibility of bait, substrate and ground cover, associated with higher catch rates for each predator group are described.