Why did introduced stoats, ferrets, and weasels harm native birds in New Zealand?

Introduced stoats, ferrets, and weasels harmed native birds in New Zealand primarily because they are bold and aggressive predators that were introduced into an environment where native species had evolved in the absence of such predatory mammals.12

These animals, which belong to the carnivore order and the family Mustelidae, were originally brought to New Zealand to control rabbit populations. However, they became invasive and began preying on native birds and their eggs. Because many of New Zealand’s native birds are flightless or ground-nesting, they were particularly vulnerable to these predators, which are highly proficient at hunting in burrows, crevices, and dense vegetation. Furthermore, because these mustelids cannot accumulate fat and must eat frequently, they often kill more prey than they can immediately consume, leading to significant destruction of local wildlife populations.231