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There are 3 types of rat in New Zealand:

  1. Pacific rat (Rattus exulans)/kiore (Māori), were introduced by Maori settlers around the 10th century. 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. In 1995 the Department of Conservation (DOC) released a kiore strategy document advocating the elimination of kiore and other rodents from islands administered by DOC, but also recognising 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 DOC’s administration) for cultural or scientific reasons.
  2. Norway or brown (Rattus norvegicus), the largest of two European rats and the most common in New Zealand. it\’s distinguished from the ship or common rat because its tail, which is 180mm long, is thicker and shorter than its body, which is 200mm long. These rats are the most problematic for braided river birds, as they swim well.
  3. Ship or common rat (Rattus rattus), the smaller of the two European rats, its tail is longer than its body and the ears are larger, able to cover the eyes when pressed forward. Length 225mm, excluding tail. Weight 120-160gm but can be as much as  225gm.
From left to right: Norway rat, ship rat, kiore, mouse: Natural Sciences Image Library of New Zealand (photo: Peter E. Smith)
From left to right: Norway rat, ship rat, kiore, mouse: Natural Sciences Image Library of New Zealand (photo: Peter E. Smith)

Why are they a problem?

Being generalist mammals, all rats are notoriously successful, fast breeders, and highly adaptable to a wide range of climates and habitats. Once established in an area, they are next to impossible to eradicate.

  • Kiore prey on invertebrates, frogs, lizards, birds and bats
  • Norway and Ship rats can kill nesting adult seabirds and riverbirds. Norway rats swim well
  • Reducing the rat population through strategies such as 1080 poisoning leads to an increase in cats and mustelids, illustrating the complexity of managing predator guilds around braided rivers

Mast Years

Rats are the primary food for mustelids and cats. When conditions are right, particularly mast years where there is a glut of food, rat numbers can explode, which in turn leads to a population explosion of longer-lived mustelids and cats, that rapidly turn their attention to native species once rat and mice numbers are depleted.

Where are they found?

Along all braided river ecosystems in New Zealand.

Conservation activities

  • The primary tool for controlling rats in New Zealand is 1080. While beech forests are targeted, there is a carry-over effect on braided rivers where the rats pass through forested areas
  • Frequently caught in The DOC 150 traps, Predator Free250 sell dedicated rat traps here.
  • If you are interested in helping out with or starting up a local trapping programme, please contact your nearest DOC office or contact one of the local river care groups
This video is a recording of the 2023 Braided Rivers Seminar presentation, Here, John Innes provides insight into the unique behavior of these rats that could help lead to better trapping and management outcomes.

More information