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Proceedings of the First Symposium on Marsupials in New Zealand

Trichosurus Vulpecula in Australia

Trichosurus Vulpecula in Australia

In Australia, the common brushtail possum Trichosurus vulpecula is not often regarded as a pest. It occurs in South Queensland, New South Wales, Victoria and Tasmania. The distribution of T. vulpecula overlaps narrowly with that of the mountain brushtail possum Trichosurus caninus, generally in dry sclerophyll forests which have an unusually dense under-storey. Broadly, T. vulpecula is restricted to dry sclerophyll forest but it is also a common suburban dweller, while T. caninus is largely restricted to wet sclerophyll, sub-tropical or rain forest (Owen and Thomson 1965). T. vulpecula feeds mainly on eucalypt leaves, which may form 66% of its diet (Freeland and Winter 1975), as well as on a variety of indigenous and exotic shrubs. It is primarily arboreal, while T. caninus feeds mainly on ground or under-storey plants; there is little or no evidence of seasonal variety in the diets of either species (Owen and Thomson 1965). Mature leaves are preferred by both species so that food availability is constant all the year round. Nest sites of the two species differ; T. vulpecula mostly up trees, T. caninus in fallen logs or hollow stumps. T. caninus is more tolerant of wet conditions than the mainland T. vulpecula, and is probably more terrestrial.

Trees in exotic plantations (mostly Pinus radiata) may be attacked by both species of Trichosurus but also by Rattus fuscipes 1, Wallabia bicolor, and occasionally by the common wombat Vombatus ursinus and the rabbit Oryctolagus cuniculus (McNally 1955). The bark of the trees is removed by all these species, with a typical pattern for each. T. vulpecula strips off the bark and eats the soft cambial flesh, and there is not much sign of bark in the stomachs. W. bicolor and R. fuscipes eat both stripped bark and apical portions. Both T. vulpecula and T. caninus may girdle the trees, which 1formerly Rattus assimilis

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causes either tree malformation or death. With T. vulpecula the damage is often much more difficult to detect because it occurs higher up in the trees. There may be repetitive attacks on particular trees. In four plantations sampled for possum damage, only 20% of the trees remained untouched (McNally 1955).

In Tasmania, Eucalytpus regnans (mountain ash) is browsed by T. vulpecula (Cremer 1969), as are Acacia and Pomaderris species. The main damage is done to trees up to about 1 metre, and it is uncertain what part of the damage is attributable to T. vulpecula and what is caused by other browsing species (e.g. wallabies). Petioles of E. regnans are eaten by T. vulpecula, with leaves appearing to be eaten mostly in autumn and winter. However, this may be an erroneous observation because it is then that browsed foliage would be least likely to be hidden quickly by new growth. Tasmanian plant species seem able to recuperate from browsing more readily and in more months of the year than most New Zealand species.

Some workers (e.g. Green 1974) consider that T. vulpecula is primarily a ground feeder in Tasmania and that it has a liking for a wide variety of food, including meat. Though formerly restricted to dense sclerophyll forest in Tasmania, it is now much more widely distributed, and despite its mortality from hunters it has increased and is now plentiful.

Troughton (1941) says that though T. vulpecula is specialised for an arboreal existence, it thrives in comparatively treeless areas, making dens in rabbit warrens, etc., as readily as in trees. He considers that in the wild state its food is variable, and includes many species of eucalypt. In Australia generally, T. vulpecula is thought to be rarely responsible for other than localised damage. The Tasmanian T. vulpecula, thought by Troughton to be a separate species (T. fuliginosus), is much heavier than its mainland grey-furred counterpart, and has much denser, longer fur which is more commonly brown.