Puketi Forest Trust, restoring and protecting the native wildlife, trees and plants of Puketi Forest in Northland, New Zealand.

Rats

There are three types of rat in New Zealand. The Pacific rat or kiore (Rattus exulans), the Norway or brown rat (Rattus norvegicus) and the ship or common rat (Rattus rattus).

The kiore or pacific rat came in waka about 2000 years ago and feasted on the undisturbed birds, insects and lizards. Kiore are now found only in Fiordland, Stewart Island and some off-shore islands.

The Norway rat is the largest of the two European rats. It arrived with Captain Cook in 1769. These rats typically weigh around 400 grams and are excellent swimmers. Norway rats do not climb trees but frequent water courses where they feed on ground-nesting birds and their young, and on other ground-dwelling animals such as lizards.

Puketi Forest Trust, restoring and protecting the native wildlife, trees and plants of Puketi Forest in Northland, New Zealand.

The ship rat, which is more common, has a tail larger than its body and ears that cover the eyes when pressed forward. Also known as the black rat, this rat is the deadliest predator of New Zealand’s native birds. An expert tree climber, it was first seen in New Zealand in 1862 and the disappearance of large populations of saddleback, stitchbird and bellbird immediately followed. Both of the European species are associated with human activity and are found in houses, tips, waterways and cropland.

For larger birds, such as the kiwi, rats are not a predator but a competitor because the invertebrate diet of rats and kiwi is almost identical; both forage for surface invertebrates. In autumn and winter ship rats spend more time on the ground and the intake of invertebrates is high and plant material low. In summer ground is harder to probe and more insects are taken from the surface. Young kiwi have short bills and depend on surface insects. Competition from rats slows the growth rate of kiwi chicks therefore they take longer to reach the weight of one kilogram when they are safe from stoat predation.

Did you know? In a kiwi territory there may be over 100 rats.