Rats, stoats, and possums kill an estimated 25 million native birds every year. They are the most damaging mammalian predators that threaten New Zealand’s natural taonga, economy and primary sector.
• Rats threaten the survival of many native species such as wētā, snails, lizards and birds. They eat almost anything, including our native species and their food sources. They are common agricultural, industrial and domestic predators, causing a great deal of economic damage and posing a risk to human health. There are two introduced European rat species in New Zealand, the Norwegian rat (Rattus novegicus) and the Ship rat (Rattus rattus) with both widespread throughout New Zealand. Ships rats tend to be more nocturnal and Norway rats more diurnal. Ship rats can be identified from Norwegian rats as Ship rats have tails longer than their head+body and have large ears which cover their eyes when pulled forward.
Both species are omnivorous, with a preference for grains. In a suitable environment rats will breed throughout the year, with a female producing three to six litters of up to 10 young. Ship rats are the most frequent predator of small forest birds, seeds, invertebrates, and perhaps lizards, in New Zealand forests, and are key ecosystem changers due to this predation. Ship rats are commonly found around buildings and farms, where they cause significant damage to any stored food or crops they are able to access.
Why is the species of rat important?
The type of rat present has implications for pest control projects. For example, having more ship rats around has implications for most tree-nesting birds including kereru and small birds. This is because they are more agile and better climbers. Norway rats on the other hand are large and ground-dwelling, with potential impacts on ground nesting species. They also prefer wetland and other water habitats (sometimes called Water Rat). Norway rats have larger home ranges than Ship rats (500m vs 150m average), which will dictate your layout of control tools if just targeting one species in your project area.
• Mustelids are a diverse group of small to medium-sized carnivores distributed throughout the world. Three species occur in New Zealand, the ferret, the stoat, and the weasel. In particular stoats have caused the extinction of several New Zealand bird species and are the major cause of decline for many other species, including reptiles and invertebrates. They attack defenseless young kiwi and contribute to the continuing decline of mainland kiwi populations.
• Possums eat many native species including snails and beetles as well as native birds. They decimate forest canopies and compete directly with native birds such as kiwi for food and resources. Additionally Possums spread bovine tuberculosis to cattle and deer, resulting in high costs and lost productivity. They also harm horticulture and commercial forestry crops.