Possums: know your pest!

Brush-tailed Possum: (Trichosurus vulpecula)

Identification and habitat
Brought into NZ from Australia in 1837 to establish a fur trade, possums cause significant problems for forest canopies, native wildlife and are carriers of bovine TB. They are cat-sized marsupials with thick bushy tails, body fur, pointed snouts, large, fox-like tapering ears and brown eyes. They can be a variety of shades of grey to brown, but some lighter variants exist in pockets around the country.
They range in weight from anywhere between 1.4 and 6.4 kg.

Habitats
They are able to live in a wide variety of habitats and are only limited by shelter and food supply. Home ranges vary from 0.6 to 3.4 ha and their preferred habitat is forest. They can get to very high densities in podocarp-broadleaf forests and pasture-forest margins.

Behaviours
They are opportunistic omnivores, which means that they are largely herbivorous (eating leaves, berries and nectar) but will eat eggs, chicks and invertebrates if they come across them.

• Possums are largely arboreal (live in trees) and are nocturnal meaning and sleep in dens, tree branches, hollows, building cavities and may have several in their area. Much of their time is spent in trees but they will spend approx. 10-15% on the ground.
• Larger males become dominant and will control food sources in their areas from smaller males.
• Main breeding season is autumn, but occasionally there is a second breeding attempt in spring.
• Possums are interested in new things in their environment (neophilic). They are attracted to bright colours, reflectors, new objects and smells.

Threats – why are they a problem?
A major long-distance spreader of bovine TB. The value of loss of primary production due to the damage done by possums and their control run in to the tens of millions of dollars. In order to compete successfully in internal export markets, New Zealand must satisfy trading partners through inspection and certification, failure to provide these could see trade embargoes on meat exports. 

• Possums have been recorded traveling long distances to consume winter feed crops while clover and grasses are eaten in large quantity throughout the year. Past studies have reported that along bush/pasture margins, up to 30 percent of possums diet is pasture. 
• Eight possums are equivalent to one sheep, hence 2 or 3 possums per ha on farmland can represent a significant loss of production.
• They can cause extensive damage to new plantations of Pinus radiata.
• Possum impacts on horticultural production is widespread although seasonal (i.e. when flowering and fruiting).  Ornamental plants such as roses and flowerbeds are readily eaten by possums, making gardening frustrating for some keen gardeners.
• One of the primary causes of forest canopy collapse, death of the upper layers of the forest canopy, in New Zealand. They eat the young shoots/leaves and prevent regrowth, sometimes resulting in the death of the tree or plant.
• They occur in NZ in high numbers due to the absence of any predators in this country and the abundance of food.
• They are significant food competitors for native species. They eat most of the new shoots, flowers and berries that are essential for birds, lizards and invertebrates to survive.
• They eat eggs and chicks of native birds and will use nesting sites as dens.

There is an estimate of 460,000 possums over the 115,000 ha of Banks Peninsula.
At 4 possums/ha that’s 92,000 possums across the 23,000 ha of the Extended Wildside.

Possums are New Zealand’s most well-known pests with an estimated 30 million yet to be caught.
We are on the job!

In 1946, possums were officially declared a pest in the New Zealand environment. By 1950 possums were found in over half of New Zealand and they kept spreading.