Rats in Northlands Forests

Introduction to rats

Fantail chicks bring eaten alive by a rat

Rats have a major impact on the forest and are present in large numbers. They need to be reduced significantly.

Rats are omnivorous, eating native animals and their eggs plus a wide range of native fruit and plants. By eating the seeds, fruit and leaves, rats modify forests ecosystems leaving native wildlife with an insufficient food supply.

Controlling rat populations will reduce the damage to native plants, birds, Kauri snails, lizards and insects, promoting forest regeneration.

Multiple Species of Rats in New Zealand

There are three species of rats in New Zealand, all of which have been introduced:

• Kiore, Rattus exulans,
• Norway Rat, Rattus norvegicus, and
• Ship Rat, Rattus rattus.

All three of these rats have slightly different niches and impacts on the forest but all are destructive and need to be controlled or eradicated.

Rats Arrival in New Zealand

Kiore Rats

originated in Asia and were spread around the Pacific in the canoes of Polynesian seafarers, arriving in New Zealand around the 13th century.

Once prominent throughout New Zealand, Kiore numbers declined when Norway Rats, Ship Rats and Mice arrived in the New Zealand with Europeans and competed with the Kiore for the same food. By the early 1920s Kiore were thought to be extinct, however some survive in Fiordland, on Stewart Island and on several offshore islands.

Norway Rats and Ship Rats

arrived in New Zealand in the late 1700’s on sailing ships from Europe. Once here, they rapidly spread across the country

Description of New Zealand’s Rats

The table below summaries the physical differences between the species that can be used to identify them.

Rats Habitat

Kiore

live in holes in the ground or in hollows in tree trunks emerging at night to feed. They tend to live mostly in forest areas.

Norway Rats

Have a patchy distribution and tend to be found in urban areas around human activity although they have also been found on more than 60 off-shore islands around New Zealand.

Ship Rats

Are the most common rats in New Zealand. They are widely dispersed throughout the country and found in almost all the different environments New Zealand has to offer.

Rats Diet

All three types of rats are omnivorous, opportunists and not overly fussy. Rats in urban areas will eat whatever their neighboring humans make available but rats in the forest tend to focus on certain things:

• Fruit and berries, including those from Miro, Tawa, Karamū, Taraire, Karaka, Kohekohe, Kawakawa, Pūriri and Patatē.
• Insects; including Wētas, beetles, spiders, Pūriri Moths, cicadas, Kauri Snails,slugs, lizards
• Birds; both the young and the eggs.

They are great climbers although Norway Rats prefer the ground. Rats will use this climbing ability to access bird nests where they will eat the eggs and young chicks.

The Kiore’s preferred food seems to be fruit and berries. Their favourite is the Hīnau berries, but they will eat a wide range of berries from native trees. They are also very keen on the tāwhara fruit from the Kiekie plant. Māori were also rather keen on this fruit and used to keep the Kiore out by gathering up the long leaves of the Kiekie and tying them over the fruit to create a barrier.

Rats that have recently killed and eaten a native Kauri Snail.

Rats Effect in the Tangihua Forest

All three of the types of Rats will kill and eat native insects and invertebrates like Weta, Skinks and Geckos. They are a double threat to birds; competing with them for the insects, fruit and berries the birds rely on and raiding nests and eating the eggs and young birds. Eating the fruit and berries also prevents the seeds within from germinating so the next generation of trees and plants are not given a chance to grow.

Kiore

the first to reach New Zealand arrived to find an abundance of wildlife that had little to no defences against them and it seems that Kiore made the most of it. They are thought to have been responsible for the extinction or significant reduction of a range of different types of native animals, insects and birds.

Norway Rats

As they are the largest species of rats and mostly ground dwelling, pose the biggest threat to native species that live, feed, roost or nest on the ground. They frequently target large invertebrates and can lead to the local extinction of these species.

Ship Rats

Are considered to be the rats that do the most damage to New Zealand forest birds. They are skilled climbers, invading nests and nesting hollows and eating the eggs, chicks and even the parent on the nest.

Other detrimental effects on the forest e.g Masting years

Mast years are when certain types of conifer trees produce huge amount of seeds in the same season. This massive abundance of food allows rats to reproduce at rapid rates. Rats can produce a litter of 5 to 8 pups every six weeks and within 12 weeks the pups are mature and can start breeding as well.

Research has shown that in a beech forest during a mast year, rat numbers can increase by as much as 1.2% per day, or 35% in a month.

When the food supply runs low around November, the rats then turn to other sources, such as the native birds that are nesting around that time of year.

Masting in Northland forests by Dean Baigent-Mercer.

Conservation strategies

Rats are present in large numbers in the Tangihua Forest and all through Northland. Their numbers need to be reduced significantly because of the major impact they have on the forest.

The easiest way to reduce rat numbers in an area as large as Northland’s Tangihua Forest is by poisoning. They can also be caught in traps with bait, but usually the Mustelids beat them into the traps.

Kiore have been poisoned along with other rats. Māori consider the species significant because they were purposely brought here by tupuna so Kiore will be allowed to survive on two islands that form part of Northlands Hen and Chickens group.

The Tangihua forest block is managed by the Department of Conservation (DOC). They currently do not have the funding available to put in place the strategies needed to eradicate pests and protect the forest. They provide the bait for the bait station and fill half of them. Tangihua lions lodge conservation volunteers fill the other half. They currently do not have the funding available to put in place the strategies needed to eradicate pests and protect the forest.

The Tangihua Lions Lodge has set up the following programs that you can be a part of;

• Tangihua Community Pest Control Area: Targeting pests on farmland with local farmers and the Northland Regional Council
• Conservation on DOC Land: Tangihua Lions Lodge Conservation and Education project
• Conservation Education: Creating a high quality, accessible educational center surrounded by a fully functional ecosystem for schools and anyone else who may choose to use the facility.
• Volunteers Options: How you can help protect our native bush.

We have set up monitoring stations see Monitoring stations. We have some for our own use and other for students.

We have a poisoning system in place we here we have a combined possum and rat bait stations covering 450ha see bait stations.