Straddling the divide: den use by brushtail possums (Trichosurus vulpecula) in urban parklands

In Australia, brushtail possums (Trichosurus vulpecula) are declining in natural habitats but have adapted to urban environments so readily that some human residents consider them to be a nuisance. Although this situation represents a conundrum for management, the use of urban habitats by the species remains poorly studied. We conducted our study in six urban parklands, a setting that represents an intermediary between a fully-urban and fully-natural environment. To determine factors that influence the presence of hollows in trees and their use by brushtail possums, physical characteristics of 240 mature trees in six parks in the Adelaide Parklands, South Australia were assessed. To investigate hollow use more comprehensively, 18 possums were radio-tracked. Presence of hollows in trees was a function of tree species and tree size, with hollows formed in both exotic and native species. Tree form and number of hollows were significant predictors of the use of hollow-bearing trees by possums. Use of exotic trees was high, with only 34% of recorded den trees being native (non-indigenous) species. Radio-tracked individuals were relatively sedentary, with an average daytime denning area of 0.08ha. While the majority of animals used multiple den sites, all individuals favoured a single den. Use of a variety of anthropogenic structures was high, even when trees were available. On average, sites supported ~1.5 brushtail possums per hollow-bearing tree. A correlation between number of hollows per hectare and possum density (r =0.892, P =0.017) suggests that altering a given area's density of hollows or anthropogenic structures could influence the density of possums within it.