The Australian brushtail possum (Trichosurus vulpecula) has been blamed for the decline of three native New Zealand beech mistletoe species (Alepis flavida, Peraxilla tetrapetala and Peraxilla colensoi, Loranthaceae), but there are few quantitative data on possum effects, and anecdotal evidence is often conflicting. We present results from two monitoring programmes that suggest possum control operations can improve mistletoe health.
A long-life poison bait dispenser, consisting of a tree-mounted platform that dispenses a highly attractive liquid bait only when triggered by actions characteristic of a possum (Trichosurus vulpecula), was developed. The liquid bait formulation prevents deterioration due to the action of oxygen, moisture, bacteria and insects. The prototype is designed to dispense 100 lethal doses of poison, and is expected to last more than five years in the field without attention. The equipment is designed to avoid fouling by algae, debris or nesting insects.
Vertebrate pest control operations using toxic baits can have unintended consequences for nontarget species. some of which may themselves be pests. Learned avoidance behaviour (termed 'aversion') can be induced by sublethal dosing, which can arise when species with high and low susceptibilities to a toxin co- exist in the same area. In such cases the less-susceptible species (e.g., possums Trichosurus vulpecula) may be sublethally poisoned by control work targeting the more- susceptible species (e.g., rabbits Oryctolagus cuniculus).
Poisonous baits used for pest control in New Zealand commonly contain green dye and cinnamon oil to make them less attractive to birds. Research aimed at reducing the impact of poison based pest control on birds has shown that some birds are initially deterred from feeding on blue or, to a lesser extent, green coloured food and are attracted to yellow or red food. We determined whether colours that deter or attract birds affected the acceptance of non-toxic and toxic cereal baits by captive brushtail possums (Trichosurus vulpecula).
Fuchsia (Fuchsia excorticata) has been heavily browsed and often killed by brushtail possums (Trichosurus vulpecula) in many New Zealand indigenous forests, but remains healthy at some sites despite long histories of possum occupation. To determine whether fuchsia varied genetically in its palatability to possums, material from six widely dispersed stands (provenances) was propagated, and leaf chemistry, leaf morphology, growth rate, and palatability to captive possums was compared.
To assess the effect of possum browse on plant growth, an index of the amount of foliage on about 50 trees of Fuchsia excorticata and the number of trees that died or were completely defoliated was measured at five sites in South Westland over 5 years. This index was compared to possum density indices taken at each site each year. At one site, possums were reduced from a high density about 6 months before the final measurement. The degree of defoliation of fuchsia was significantly related to the density of possums at each site.
Two techniques for assessing possum (Trichosurus vulpecula Kerr) diet from stomach contents ("point-sampling" and "layer- separation") are described and compared. Point-sampling involves sieving stomach contents, systematically selecting fragments from the retained material then, identifying and weighing these. Layer-separation involves separation, identification, and weighing of the discrete layers apparent in most possum stomach contents. In 41 of 43 stomachs examined, we were able to separate discrete layers that nearly always comprised a single food item.
The seasonal variation in possum browse and foliage cover of five possum-preferred species was quantified and studied in northern Westland, New Zealand over a 24 month period. Four of the five species (Pseudopanax simplex, P. colensoi, Aristotelia serrata, and Elaeocarpus hookerianus) showed marked seasonal patterns in both browse and foliage cover, with maximum browse evident in winter/spring when foliage cover was at a minimum. There was very little browse and no seasonal pattern in foliage cover for the fifth species, Pseudopanax crassifolius.
Possum leaf diet from 1976 to 1989 in the Orongorongo Valley was compared with the diet recorded from four previous years, using faecal analysis. There were large differences in the proportions of species eaten in different seasons and between different years. There was little overall change in the proportion of the main diet tree species, Metrosideros robusta and Weinmannia racemosa, and seasonal increases or declines in one were usually balanced by opposite changes in the other.
Food of the North Island kaka (Nestor meridionalis septentrionalis) on Kapiti Island was identified while quantifying the foraging activity of nine radio-tagged birds from March 1991 to January 1992. Additional food types were identified by opportunistic observation of feeding birds and qualitative examination of nestling faeces. A diverse range of food was taken, including wood-boring invertebrates, scale insects, seeds, nectar or pollen, fruits, and sap.