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Proceedings of the First Symposium on Marsupials in New Zealand

Introduction

Introduction

The common brushtail possum Trichosurus vulpecula has long been recognised as a harmful browsing species in New Zealand's indigenous forest. In addition, in the last decade it has been identified as both a vector and reservoir of two diseases of farm stock, namely bovine tuberculosis and leptospirosis, and to be an important competitor of farm stock for both pasture and fodder crop species.

The control of possums foraging out onto farmlands relies heavily on the extensive use of compound 1080 applied to vegetable baits and sown throughout adjacent forests. The dramatic rise in control costs (see Coleman, this symposium) increases the need to maximise the percent kill; in particular the need to control that proportion of the possum population which is most "at risk" to Tb. infection. A more efficient approach to aerial control with 1080 clearly requires better information on the ecology of possums in page 52 forest/pasture margin situations. With this control objective in mind we started studying the foraging patterns of possums with the intention of defining the zone of contact on forest/pasture margins between possums and stock, and thus delimit more accurately the width of the adjacent forested slopes requiring control.

The study discussed here is continuing on the slopes of Mt Bryan O'Lynn near Lake Haupiri in central Westland, and involves possums on a 800 m wide strip of land extending from improved stocked pasture at 230 m to alpine grasslands at 1350 m altitude. In this paper we discuss the broad patterns of population movements between forest and pasture, and the implications of these movements from a control perspective. Further seasonal details of movements, other aspects of possum biology, and the interaction between possums and rata/kamahi (Metrosideros/Weinmannia) forest will be published at the completion of the study.