Diet of Brushtail Possums over a Pasture-alpine Gradient in Westland, New Zealand

The diet of brushtail possums (Trichosurus vulpecula Kerr) in mixed hardwood forests on a central Westland hillside is described from analysis of plant cuticle fragments and seeds in their faeces. Faeces were collected monthly for 2.25 years from animals live-trapped from low altitude forest/ pasture margins through to high altitude alpine shrublands. The diet included forest and pasture foliage, buds, and fruits of over 100 species, although most were eaten infrequently. Foliage was taken most often from woody forest species (88%), with three canopy species, kamahi (Weinmannia racemosa), southern rata (Metrosideros umbellata), and mahoe (Melicytus ramiflorus), providing 69% of the leaf intake. Pasture species formed 12% of the diet of possums living within 300 m of the forest edge, with 90% of this being clovers (Trifolium spp.) and grasses. Fruit was taken from a wide range of forest species. Diet varied with sex, season, and altitude. Males ate more pasture foliage and less ferns than females and differed significantly in their use of many of the major woody species. Woody species were favoured most in winter and spring, ferns and fruits in autumn and winter, and pasture species in autumn. Pasture species were eaten only by possums denning within 1000 m of the forest/pasture margin, and high-altitude species by possums denning nearby. Only 15 forest species were eaten as much as or more than expected from their relative abundance. Ten of these species were frequently eaten, and the remainder infrequently, being locally rare. Preferred species showed clear evidence of possum browse and were often represented by many dead stems. This demonstrated the adverse effects of possums in such mixed hardwood forests.