Movement of Possums (Trichosurus vulpecula) between Forest and Pasture in Westland, New Zealand—Implications for Bovine Tuberculosis Transmission

Over a 3-year period, 1183 brushtail possums (Trichosurus vulpecula) were live-trapped in 125 ha of mixed hardwood forest and adjacent pasture in Westland, and 50 were radio-tracked for up to 14 months. Foraging movements between forest and pasture were much longer than previously reported. Twenty-eight percent of males and 18% of females denning c. 1000 m into forest were trapped on pasture at least once a year. These values were higher for possums denning closer to pasture, but dropped abruptly at distances beyond 1000 m and ceased beyond 1300 m into forest. Radio-tracking confirmed the trapping results and showed that possums travelled to and from pasture within the same night.
Age had little influence on travel to pasture, but males were twice as likely to travel as females. Pasture travel peaked in summer and autumn, coinciding with maximum pasture growth. Possums usually travelled less than 300 m beyond the forest edge, but foraged occasionally to 1300 m.
Possums moved vertically rather than horizontally across steep terrain, thereby minimizing travel between different food sources in the vertically stratified forest. Forest residents travelling furthest were those with dens 600-1000 m into forest. Consequently, control of possums in Tb-problem areas will be required over forest at least 1 km in from forest-pasture margins. Changes in farm management that reduce possum-cattle interactions are also desirable.