Rats

Ship or common rat. Photo: Herb Christophers.
Ship or common rat

Rats are introduced pests which threaten the long-term survival of native species. They include the Pacific rat/kiore, ship or common rat and Norway or brown rat.

Kiore, introduced by early Maori voyagers, predate rare weta, snails, frogs, lizards, tuatara, birds and bats, as well as other insects and the flowers, fruits and seeds of plants.

Ship rats and Norway rats also eat any small animals and plant material, including the adults, eggs and chicks of many rare birds.

Facts

There are three types of rat in New Zealand.

Pacific rat/kiore

Pacific rat/kiore (Rattus exulans) are now found only in Fiordland, Stewart Island and some off-shore islands. They were introduced to New Zealand by Maori settlers and have cultural and spiritual values to some Maori.

Kiore. Photo: Dick Veitch.
Kiore (Pacific rat)

Kiore is the Maori name for a species of rat (Rattus exulans). It is the world's third most widely distributed rat, found throughout the Asia/Pacific area. Kiore are poor swimmers and have reached New Zealand mainland and offshore islands through deliberate and accidental introduction by humans.

They were introduced to New Zealand by Maori settlers in about the 10th century.

Kiore are restricted in New Zealand to Fiordiand, Stewart Island and a number of offshore islands. Of the many introduced mammals to New Zealand, kiore are unique because of their association with the migration of Polynesians throughout the Pacific and because of their cultural and spiritual values to some iwi Maori.

Kiore eat a wide range of foods including seeds, fruits, insects, lizards, eggs and chicks. New Zealand's native plants and animals, however, evolved in the absence of mammalian predators and are therefore poorly equipped to compete with, or defend against the impact of introduced species.

In 1995 the Department of Conservation released a kiore strategy document. That strategy advocated the elimination of kiore and other rodents from islands administered by the Department.

At the same time the strategy recognised the cultural and spiritual value of kiore to some iwi Maori and acknowledged that kiore were likely to remain on the mainland and on some islands (outside of the Department's administration) for cultural or scientific reasons.

Kiore (Pacific Rat) are widely distributed throughout the Pacific and South East Asia. In New Zealand they are found in Fiordland, Stewart Island and some offshore islands. The Department of Conservation administers approximately 230 of the estimated 600 islands around New Zealand. Fifteen of these islands have kiore.

Removal of kiore from all 15 of Department administered islands would reduce their New Zealand range by only four per cent.

Kiore are not protected under New Zealand statutes.

Evidence suggests kiore eat seeds and fruits, lizards, insects and the eggs and chicks of native birds. Where they are removed from offshore islands, considerable conservation gains are possible.

The Department of Conservation has successfully eradicated kiore (and other rodents) from a number of offshore islands and plans to pursue eradication for all fifteen islands under its administration.

Recognising that iwi Maori sometimes have a cultural interest in kiore, as well as the ecological health and well-being of plants, forests and wildlife, it is the Department's practice to consult prior to eradication programmes.

Various methods have been used to eradicate rodents from offshore islands including trapping, 1080 and talon-type baits. Recent advances, including the development of more effective anticoagulant poisons and new application methods, mean it is now possible to consider rodent eradication operations on larger islands. The Department, health and regional authorities are involved in poisoning operations to ensure risk to humans, the environment and non-target species is minimised.

Ship or common rat

By contrast the ship rat (Rattus rattus), which is more common, has a tail larger than its body, and ears that cover the eyes when pressed forward. Both of the European species are associated with human activity and are found in houses, tips, waterways and cropland.

Norway or brown rat

The Norway rat (Rattus norvegicus) is the largest of the two European rats. It is distinguished from the ship rat in that the tail, which is about 180 mm in length, is thick and shorter than the body, which is about 200mm in length, and that the ear of this rat does not reach the eye when pressed forward.

Norway rat. Photo: Rod Morris.
Norway rat

The threat

Ship rat in Fantail nest. Photo copyright: David Mudge (DOC USE ONLY).
Ship rat in Fantail nest

Rats have a major impact on New Zealand’s wildlife because they eat birds and their eggs and chicks, lizards, and invertebrates. They also eat a wide range of native fruits and other plant material, which puts them in competition with native wildlife for food.

Ship rats are causing the most damage to our wildlife because they are good climbers, so they are able to get access to most bird nests high in trees. Norway rats are large enough to kill nesting adult seabirds and prey on animals that live, roost or nest close to the ground. 

Kiore eat a wide range of foods, including seeds, fruits, lizards, insects, eggs and chicks.

DOC's work

Rodents and other predators have been eradicated from several offshore islands which, as nature reserves, are now safe havens for many rare and endangered species.

On the mainland, six official "mainland islands" have been established. These are areas of intense predator management, making them also safe for vulnerable species. But pest control is on-going throughout DOC managed land.

Suppressing rats protects birds

1080 poison can suppress rats when seed production in New Zealand forests causes rodent irruptions. When this happens huge numbers of native birds are killed by rats and stoats. Scientist Graeme Elliott explains in this video:

1080 poison helps protect native bats from rats

New Zealand's bats are rapidly heading towards extinction caused by rat plagues.

In this video Dr Colin O'Donnell explains how biodegradable 1080 poison protects bats on a scale unmatched by rat trapping.

1080 poison helps suppress a rat plague and protect native parakeets

This video shows that in the Maruia Valley nine parakeet nests were monitored though a 1080 operation designed to suppress a rat plague in November 2009. One nest was eaten by either a rat or a stoat the other eight were fine.

In places where 1080 has not been used to stop rat plagues, entire populations of parakeets have been destroyed by predators.

Videos by Trakabat

You can help

Signs that rats are present

Remains of food such as seeds or snail shells can be found under cover like hollow logs, or amongst tree roots. Sometimes nests of loosely woven twigs and leaves can be found in tree holes, or in burrows in the case of Norway rats. Droppings are cylindrical and stubby, sometimes tapering to a point. Norway rat pellets are about 16mm long, roughly twice the length of other rat pellets.

Norway rats excavate burrows 60-90 mm in diameter, often beneath cover such as rocks or tree roots. They can excavate large volumes of soil, and often hoard food in their burrows. Pathways 50-100mm wide link burrows with feeding sites, and these paths can become well worn trails.1

Methods of control

Rat with poison bait, Fiordland National Park. Photo: DOC.
Rat with poison bait, Fiordland National
Park

Rats populations fluctuate. Numbers will suddenly increase every five or seven years and it is at these peaks that major damage occurs. Regular control will keep rat populations at continuous low levels. Control methods include trapping, poisoning and the use of predator proof fences.

Training

If you are planning a pest control operation enrol for the Animal Pest Control Methods field based course.

The course provides an overview of animal pests, their impacts and control methods (including the principles these are based on, and the task specifications DOC has developed).

The course covers all the legal requirements for animal welfare and handling toxins. Working within the law is vital to allow pest control agencies and community groups continued access to the full suite of animal pest control methods.

In particular, it describes the control methods most commonly used in DOC, and their advantages and disadvantages.

Watch a video

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