Ship and Norway rats and kiore have a major impact in New Zealand because they are omnivores – eating birds, seeds, snails, lizards, fruit, weta, eggs, chicks, larvae and flowers. The varied diet of rats also makes them competitors with native wildlife for food sources.
Possums have a significant impact on many of New Zealand’s natural ecosystems. They occur in high numbers and their own predators, such as feral cats, do not have much effect on controlling possum population size. Leaves are the main part of their diet, but possums are opportunistic omnivores. They eat buds, flowers, fruit/berries and nectar, which means they compete with native birds and reptiles for food sources.