Braided River status
Found along all braided river ecosystems in New Zealand
There are three types of rats in New Zealand
- 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.
- Norway or brown (Rattus norvegicus), the largest of two European rats, is 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.
- Ship or common rat (Rattus rattus), the smaller of the two European rats, it’s 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.
Photograph by Peter E. Smith
Why are they a problem?
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
- 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
- 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 they pass through forested areas
- While stoats are primarily targeted along braided rivers, rats are frequently caught in traps
- If you are interested in helping out with or starting up a local trapping programme, please contact your nearest DOC office, enrol in DOC’s animal Pest Control course, or contact one of the local rivercare groups.