Brushtail Possum (Trichosurus vulpecula)
History and distribution
The common brushtail possum (Trichosurus vulpecula) is a solitary, nocturnal and arboreal marsupial, endemic to Australia. In Australia, T. vulpecula are found in five disjunct groups: northern, eastern, central, and south western mainland Australia, as well as Tasmania. The taxonomic status of these groups is not fully resolved but there have been at least four subspecies recognised: T. v. arnhemenis (northern populations), T. v. johnstonii (north-eastern populations), T. v. fuliginosus (Tasmanian), and T. v. vulpecula (eastern, central and south-western populations). Trichosurus v. arnhemenis has, at times, been considered a separate species.
In Australia, they have declined in parts of their range, particularly in arid regions but have adapted well to many urban areas. In the 1800s, around 200 brushtail possums were introduced into New Zealand from Tasmania and parts of south eastern mainland Australia for the fur trade. They now number in their tens of millions and are found in most parts of New Zealand with the notable exceptions of the mountainous terrain of Fiordland, the upper slopes of Mt Taranaki and Mt Ruapehu and most offshore islands. They have become one of that countries’ most serious vertebrate pests.
Adult brushtail possums typically weigh around 2 to 3 kg with little size difference between the sexes. They are opportunistic feeders eating a wide variety of food that includes leaves, buds, flowers, fruits, ferns, bark, fungi, invertebrates, and meat such as birds and their eggs. Possums spend their daytime under cover in dens, usually above ground, and will use several dens within their home range. They may spend one to several nights in each, emerging shortly after sunset and spending the evening feeding, grooming, travelling or just sitting before returning before sunrise.
Females may breed at 1 year of age whereas males mature at 1 to 2 years with births tending to be seasonal in response to changing day length. Most births occur in autumn where typically a single pouch young is produced after 17 to 18 days pregnancy. Some females may breed twice within the same year. The young spend their first 70 days permanently attached to a teat in their mother’s pouch and are weaned and independent at 6 months. Although adults generally maintain relatively small home ranges of around 1 to 2 hectares, they may move distances of over 1km to feed and sub-adults may move more than 10 km when dispersing from the site where they were born.
In New Zealand, brushtail possums are considered one of that country’s most serious mammalian pests. Of most economic significance is the role played by possums in the transmission of bovine tuberculosis. The control of possums has become an essential element in the New Zealand government’s attempt to control and eventually eradicate bovine tuberculosis. In addition, the presence of possums in their millions has caused dramatic changes in the composition and structure of New Zealand’s native forests through the selective browsing of many species of native plants. Possums also prey on the eggs and chicks of native birds.
Current control in New Zealand is based largely on poisoning using aerial and ground application of toxic baits. The most common poison used is sodium monofluoroacetate (1080) incorporated into cereal-based pellets or coated on to carrots and then applied either aerially or as a ground-based poisons. Aerial baiting enables possum control in large areas of land that are otherwise inaccessible whereas ground baiting can be used to target specific areas and those visited frequently by people. Other methods of control include poisoning with cyanide and the more traditional hunting and shooting. The widespread application of poisons for possum control is controversial through the public perception that it poses an unacceptable environmental risk. Other methods of control including biological control are currently being investigated. In Australia, possums are protected in all states although hunting (under license) is permitted in Tasmania for the commercial use of skins and meats.
- Montague, T.L. 2000. The brushtail possum: biology, impact and management of an introduced marsupial. Manaaki Whenua Press, New Zealand.
- “A pest of plague proportions”