Species

Rattus rattus

Threats Status

Unwanted Organism

Common Name(s)

Ship rat, black rat, roof rat

Family

Muridae

Habitat

Ship rats inhabit a diverse range of habitats from coastal areas up to the tree line, but are most abundant in lowland podocarp-braodleaved forest. They are also can be found in urban habitats. Ship rats are omnivorous generalists with the main animal food being arthropods (particularly weta) but through to the high density compared to other predators the loss of eggs, chicks and adult birds (e.g. robins, tits and female mohua) is significant for the conservation concern of these species. Fruit are taken particularly from Cporpsma spp., hinau, karkaka, kiekiem, kohia, miro, matai, nikau, rimu, pate and supplejack and where these species are absent ship rats tend to prey more on invertebrates (especially in winter). They are agile climbers and average swimmer (300m).

Description

Norway rats are the largest rat species in New Zealand. They have a sleek and slender body, dark grey tail, thin hairless ears and small eyes. Their coat may vary between a black back and grey belly (‘rattus’ type), grey-brown back and grey belly (‘alexandrinus’ type) or grey-brown back and white belly (‘frugivorus’ type).

Similar Species

Ship rats may be mistaken for the other two species of rat in NZ: Norway rat (Rattus norvegicus) and Kiore (Rattus exulans).

Threat To Plants

Collection of seeds may alter the regeneration of these species, however they may also enhance the dispersal of other. Prey on invertebrates and the young, eggs of birds may also have secondary effects on the vegetation due to changes in ecosystem processes.

Distribution

Widespread over a diverse range of habitats on both the North and South Island. Ship rats also occur on many offshore islands.

Measurements

Weight: 120-160kg; max. head to body length: 225mm

Year Introduced

Approximately 1830 - 1850

Reason For Introduction

Accidentally

Colonisation History

First introduced to New Zealand between 1830 - 1850 when they were the dominant rat species aboard sailing ships, however a few individuals may have got ashore at an earlier time. For unknown reasons they did not spread in either of the two main islands until after the late 19th century. Is also uncertain if the decline of kiore led to the widespread distribution of ship rats today.