<i>Trichosurus vulpecula</i>

Percentage non-toxic bait interference is currently used by local authorities to monitor brushtail possum control operations but the validity of the method has not been established. Two models have been proposed to estimate an index of possum density (possums per bait) from a log-transformation of percentage bait interference. In two trials, percentage bait interference and the density index derived from percentage bait interference using the Bamford (1970) model usually increased from night to night.

We examined possum trapping data collected from 1945 to 1989 in the Pararaki catchment to assess whether there was any evidence for a major natural decline in possum numbers several decades after colonisation and whether the population has subsequently shown any long-term trend in abundance. The catchment was probably colonised by possums around 1915-20. We found evidence for a major decline (c. 80%) in possum numbers between 1945 and 1965. There was no significant trend in our trap catches from 1965 to 1976, but in 1977 there was a further abrupt decline.

Bird populations were monitored for one year (October 1990- October 1991) to determine whether the 1080 poison used to eradicate possums and wallabies on Rangitoto Island had had any detrimental effects on them. There was no significant decline in bird numbers recorded immediately after poisoning, with four species increasing in abundance (P <0.001). Twelve months after the operation the abundance of four species had increased significantly (P <0.001).

An estimate of intrinsic rate of increase (r(m)) of a brushtail possum (Trichosurus vulpecula) population was calculated from the measured increase in possum numbers after a poisoning operation in Westland rata/kamahi forest. Our empirical estimate of r(m) (0.22—0.25) was lower than published estimates for this species (0.30, 0.34, 0.59). Consequently, the control operation was effective for longer than predicted by population models that used these published values.

Two morphological types of brushtail possum (Trichosurus vulpecula) were introduced to New Zealand: smaller, grey possums from mainland southeastern Australia, and larger, black possums from Tasmania. Analysis of patterns of allozyme variation and allele frequencies of present-day possum populations in New Zealand and southeastern Australia indicates that populations comprised predominantly of black possums remain genetically similar to possums in Tasmania, whereas predominantly grey populations are genetically closer to Victorian and New South Wales possums.

Increased dieback in Westland rata (Metrosideros umbellata)-kamahi (Weinmannia racemosa) forests has been linked to the build-up of populations of the Australian brush-tailed possum (Trichosurus vulpecula). Within these forests young even-aged stands are observed to be more resilient to dieback than older stands. The effect of possum browsing on individual rata trees was related to the level of defoliation. Trees which had been not or only lightly browsed maintained intact canopies.

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.

Brushtail possums were studied over a period of four years by live-trapping, poisoning and kill- trapping on an altitudinal transect (455-1500 m a.s.l.) in beech (Nothofagus) forest in South Island, New Zealand. There was a single breeding season in autumn in which most females (including 80% of one-year- olds) panicipated. Trap-revealed ranges of adults were up to 1 km long and some immature males dispersed up to 10 km. Capture rates in live-traps were highest in beech/podocarp forest at 455-460 m a.s.l. and declined with altitude.

A knowledge of the sensitivity of the brushtail possum (Trichosurus vulpecula) to 1080 poison is important as a basis for planning effective control campaigns. This study assesses the effects that experimental procedure may have on determining the LD50 of 1080 for brushtail possums and reports on the variation in sensitivity within and between different populations of the species in Australia, where it is indigenous. LD50s obtained ranged from 0.39–0.92 mg kg-1, with 95 % confidence limits of from 0.29–1.20 mg kg-1.

The diet of the North Island kokako (Callaeas cinerea wilsoni) was studied in three central North Island habitats, Pureora, Mapara, and Rotoehu, for three years. Possum (Trichosurus vulpecula) diet was less intensively studied for part of the same time in Pureora and Mapara. A literature review was made of the diet of possum, red deer (Cervus elaphus), and feral goat (Capra hircus). There is considerable overlap between the diets of kokako and the three mammalian browsers; leaves and/or fruit of some species are eaten by all four, e.g.