Predators
Ship Rats
Main prey: Omnivores that eat a wide variety of prey including birds, eggs, chicks, snails, lizards, wētā, larvae, seeds, fruit and flowers.
Introduced: 1860s
Habitat: Up to 1,200 meters above sea level
Home range: On average, 100−200m for females and 160−550m for males
Breeding: Rats are rapid breeders, breeding 20-30 times faster than native birds. In suitable environments, a rat can reach sexual maturity at 5 weeks of age and will breed throughout the year, with a female producing three to six litters of up to 9 – 14 young annually. Without intervention, a ship rat population will grow about 2% every day.
Ship rats are key ecosystem changers due to their broad diet and rapid reproduction. A varied diet means they compete with native wildlife for food sources. They are good climbers, so they can access many bird nests high in trees. They generally live for two to three years and can form social groups of up to 60.
Ship rats are our trickiest predator to eliminate. When we respond to a ship rat detection, we assume that the detection indicates an emerging population, rather than a single rat.
Tools we use to target rats:
Possums
Main prey: Vegetation, eggs, chicks and insects
Introduced: Around 1837 to create a fur industry
Habitat: Forests, up to 1800 meters above sea level
Home range: About 2 hectares for males and 1.3 hectares for females
Breeding: Most female possums breed from age 1 onwards. They can produce two young a season, but more usually only produce one. Autumn is the peak time for births, but a second offspring may be born in spring if food supplies are adequate.
The Australian brush-tailed possum is bad news for our forests and native species – stripping and killing trees, eating eggs and chicks, wētā and other insects.
Across New Zealand, it is estimated possums consume 21,000 tonnes of vegetation a night – that’s nearly the weight of Auckland’s Sky Tower every 24 hours. They are known to eat 70 types of native trees and can change the overall structure of a forest. Possums also compete with native birds for habitat and food and are the main source and carrier of bovine tuberculosis, or TB, a highly infectious and serious disease found in cattle and deer herds.
They were introduced to establish a fur trade, but with plenty of vegetation for food and no natural predators their numbers soared.
Research from Zero Invasive Predators (ZIP) has found possums don’t like getting their feet wet, so rivers can be useful as a barrier to stop possums invading.
Tools we use to target possums:
Stoats
Main prey: Anything that moves: rats, mice, birds, chicks, rabbits, hares, hedgehogs, possums, lizards and insects like wētā.
Introduced: In the 1880s to control rabbits
Habitat: Up to 1800 meters above sea level
Home range: 60-200 hectares
Breeding: A female stoat can have litters of up to 12 once annually, around September-October. Male stoats can impregnate females at only 2-3 weeks old – before they even open their eyes or leave the nest.
Stoats are deadly and relentless hunters who can travel large distances at great speed. Stoats don’t just kill to survive – they kill everything in sight and store surplus food for later. They are such a devastating predator because they can climb and swim, and they have good eyesight, hearing and a strong sense of smell. They have a crippling impact on native species in the project area, especially rowi/Ōkārito kiwi.
Tools we use to target stoats:
- ZIPinns
- Toxic rodents
- 1080 (through secondary poisoning)