Possums in Northland

Common brushtail possum richosurus vulpecula

The possum reached Northland in the 1960s

Possums were introduced into New Zealand in the 1850s for the fur, food and pelt industries. Unfortunately they rapidly spread, often with some help, though-out New Zealand, reaching Northland in the 1960s.

Possums are marsupials which means when they give birth they carry their young in a pouch.

There are four colour variations: silver-grey, brown, black, and gold. In Northland we have the silver grey variety

Possums are an arboreal (meaning tree-living) animal and are well adapted for climbing with their sharp claws; a hand-like back foot for grasping and a strong flexible (prehensile) tail for curling around branches. Possums also spend much time on the ground searching for food and travelling through their home range.

The possum is a nocturnal animal and has a mostly solitary lifestyle. They usually make their dens in places like tree hollows and holes in the ground, but will also use spaces in buildings such as the roofs of houses.

Possums vocalise with clicks, grunts, hisses, alarm chatters, guttural coughs and screeching. Their cackling over territorial disputes can be heard from quite a distance. Scroll down to the video for sound.

Why possums are able to spread so efficiently

Females have a home range of about 1.3 hectares, and males of 1.9 hectares. On average a juvenile possum moves 5 kilometres from the maternal den – females further than males. In the King Country two females were recorded travelling 32 and 41 kilometres from where they were born. This is why they are able to spread to efficiently

Possum reproduction and life history

Northland possums often breed twice every year. They can have a joey in the pouch and a young juvenile on their back

Both sexes may breed at one year of age but they have a higher success rate in breeding during their second breeding season.

The lasts pregnancy of 17 to 18 days. For the first 80 days of pouch life the unfurred joey is permanently attached to the teat. At 120 days the joey begins to leave the pouch and spends several months coming and going from the pouch and riding on its mothers back until it is fully weaned and independent. The possum then sets off to find a territory of its own

Possums are the most destructive pest in the Northland forest.

Northland possums eat nearly three tonnes of leaves, twigs and berries every night.

Possums strip native forests of fruit, flowers and leaves which are vital food sources for birds.

They tend to target new shoots and systematically destroy forest canopies. Possums can cause catastrophic dieback, (the complete collapse of a forest canopy) especially on tree species that possums prefer, such as Rātā, Pohutakawa and Kohukohu.

Possums often select one tree and systematically strip it eventually killing it. They feed on new shoots, making it harder for trees to recover from weather and insect damage, and slowing their growth.

Sailing or kayaking up the Northland coast the 1,000s of dead Pohutakawa trees are a testament to the destructive powers of possums.

In more diverse (conifer–broadleaf) forests, possums selectively remove their preferred species over a number of decades, changing the composition of the forest. They feed on new shoots, making it harder for trees to recover from weather and insect damage, and slowing their growth. By eating flowers, possums stop seeds forming. Many plants fail to regenerate under possum assault.

The forest trees are then replaced by shrubs that are unpalatable to possums, and the area changes from tall forest to low open forest and shrublands.

The heaviest concentration of possums is usually along the outer edges of bush or scrub.

Possums are bird Killers

Possums were considered to be vegetarian and so were not suspected of eating birds and birds eggs.

in 1993 evidence of the effect of possums on native wildlife was first uncovered. A time-lapse video camera captured possums eating the chicks and eggs of the endangered kōkako. Of 19 nests monitored over a four-year period, cameras recorded possums eating chicks and eggs in four.

Since then, possums have been caught on film eating the eggs, chicks and even adults of other native bird species, including kererū, kiwi, harrier hawk, fantail, muttonbird, and tūī. This predatory behavior has driven some species into decline. In areas where possums are not controlled, few kōkako and kererū fledglings survive to adulthood.

In a study in Pureora Forest in 1997, robins in an area treated with 1080 poison (used to kill possums) had 67% nesting success, compared with 30% in the area not treated. After a year, robin numbers had increased by 37% in the control area, compared with 16% outside.

Possums Compete with birds for food.

By eating fruits and flowers, possums deprive nectar-feeding birds like tūī, kākā and bellbirds of the high-energy food they need in key periods such as the breeding season.

Possums also take over dens that kiwi use or roosting spots used by other birds making it more difficult for them to successfully breed – sometimes their mere presence disturbs native birds in their activities.

Possums are part of the reason for the decline in Bats

Both of New Zealand’s endangered native bat species have been recorded as being attacked by possums, In the central North Island possums eat flowers of the threatened wood rose, a nectar source for short-tailed bats.

possums will take over the roosting holes bats use.

Possums eat endangered snails and invertebrates

Possums also eat endangered native snails. One possum can eat many giant Kauri snails in a single night.

study in the Orongorongo River valley near Wellington has shown that native invertebrates form an important part of the possum diet. Over half of the possum faecal pellets contained invertebrates. The most likely targets being large, slow-moving species such as giant wētā, stag beetles and weevils.

Possum control

They became a major threat to our beef and diary industry because they spread Bovine tuberculosis (TB) a chronic infectious disease in cattle. TB can spread from domestic cattle to humans through milk, meat or directly from the animals. Within the human population it can be spread in exhaled air, sputum, urine, faeces and pus, so the disease can be transmitted by direct contact.

New Zealand set up major programme to eradicate TB which also significantly reduced possum numbers. But once the (TB) was under control this program was reduced or stopped in TB free areas such as Northland.

The cost of this project is estimated at $225,000 over 5 years.

Methodology

Bait stations for Possums and Rats

The stations for the Rats and possums will be the same one. A plastic Philproof mini bait station, originally designed for possum control but adapted and currently used for both possum and rodent control by several DOC Conservancies

The station has a mesh over the front to prevent access to the rat bait pellets from anything except rats. The stations keep the bait dry avoiding bait deterioration and the bait being washed into the soil or water table

Each bait station will cover a 1ha. They be placed 100m apart on Trap lines cut 100m apart. The stations will be placed 1.2m off the ground.

For rat control RatAbate or Pinedone and Feratox cyanide for possum control.

The following is based on two applications per annum aimed at seasonal suppression of rats and possums during the breeding season for most forest birds.

2x 25 gram applications of Ferafeed 213 prefeed paste per station

2x 400 grm applications of rodenticide (Sept and Dec) – RatAbate or Pindone Rat bait

10 Feratox potassium cyanide pellets (6 in September and 4 in Dec)

Note: If the objectives include recovery of reptile and invertebrate fauna, annual costs are likely to be double as rodents will have to be suppressed continuously.

For more information about building bait stations visit Bait stations and traps

Farmland and Regional Council – The Tangihua Community Pest Control area (TCPCA)

A Community pest control area has been set up involving a group of landowners and the Tangihua Lions Trust in the Tangihua area.

This project covers approximately 1100 ha of open pasture, scrubland and native forest. The aim of this project is to assist and provide landowners and the local community with tools, infrastructure and a means to manage introduced mammalian pests and weeds species.

This project has been established to restore biodiversity values on Private land surrounding the Tangihua Forest and to enhance and support conservation efforts being carried out in the adjacent Tangihua Forest.

This CPCA project adjoins the Tangihua forest where forest restoration activities are being undertaken by the local community. This CPCA project is working in conjunction with the Tangihua Forest Restoration project (900Ha) being undertaken on conservation land within the Tangihua Conservation forest and is pivotal in ensuring this adjacent project on conservation land is successful.

The main objectives of this project are to reduce mammalian pests and weed species, and maintain pest populations at low levels allowing for the recovery of native flora and fauna.

Pest species which will be controlled through this project area are

• Possums
• Rodents
• Mustelids
• Feral cats
• Feral Pigs
• Wild ginger
• Kauri Die back

These species will be controlled through a combination of trapping, toxins, shooting and agrichemicals.

the projected cost of this project is $265,550 with an estimated $72,300 Provided by the regional council.