Charlotte Patterson, Deb Wilson, Phil Seddon, Yolanda van Heezik.

The University of Otago has published New Zealand’s first rigorous estimate of possum density in urban areas, using Dunedin as an example.

The study looked at three locations which represent different types of urban possum habitat — a forest fragment at Jubilee Park and two residential areas in Wakari and Maori Hill. Around 70 live-capture traps were set over eight days in each area.

It found possums in forest fragments are more abundant than in residential areas. At Jubilee Park, densities were estimated to be three possums per hectare, whereas in Maori Hill and Wakari, there are less than one possum per hectare. However, animals in more residential areas may be “trap-shy” meaning they were harder to capture as part of the study. Despite low catch rates, those involved reported and observed evidence of possums — such as scat, damage to trees, regular sightings, and even hearing possums in the roof. Researchers also set cameras and saw possums in backyards where none had been caught as part of the study.

Gardens that were closer to forest fragments or with more complex vegetation such as mature trees, hedges and shrubs are expected to be more attractive to possums, providing better food sources, places to hide, and den sites.

The study is a snapshot of how many possums live in urban Dunedin and their numbers will fluctuate seasonally with the availability of food and breeding. However, overall it found that possums in Dunedin are common in areas that are also home to native birds, meaning there is risk of egg predation. Possums also cause significant damage to native plants — particularly in high numbers when they can cause enough damage to create irreversible harm to trees, causing forest fragments to experience a “die-off”.

Publications

Predicting Possums: Modelling reinvasion of the common brushtail possum (Trichosurus vulpecula) within a New Zealand urban centre (University of Otago, 2020).

Habitat-specific densities of urban brushtail possums (New Zealand Journal of Ecology, 2021).

Media

Research establishes possum density in NZ’s urban environments (University of Otago, 18 August 2021)

Urban possum control work needed — study (Otago Daily Times, 18 August 2021)

Possum spotting in the city (Radio New Zealand, 23 August 2021)

New study sheds light on how many possums live in urban areas (Newshub, 24 August 2021)