Introduced to New Zealand later than most other introduced predators (King 1984), after serious damage to native birds had already been done, stoats (Mustela erminea) contributed to the collective toll, especially in more remote areas of South Island (King and Murphy, 2005). M. erminea has been shown to be responsible for catastrophic losses of kiwi chicks in most years (see Apteryx australis; Apteryx haastii; Apteryx mantelli; and Apteryx owenii in IUCN Red List of Threatened Species) (Basse et al. 1999), and of hole-nesting forest birds in southern beech forests during periodic mouse irruptions (O'Donnell 1996). Once kiwi chicks reach a weight of around 800g they are able to defend themselves against stoats (McLennan et al. 2004) so kiwi nurseries have been set up where kiwi chicks are translocated to areas with heavy stoat control until they become large enough to defend themselves against stoats. Cost of research and management of stoats in New Zealand runs into millions of dollars a year.
Location Specific Impacts:
Predation: The Kea (Nestor notabilis) is listed as 'Vulnerable (VU) in the IUCN Red List of Threatened Species. The Kea used to be hunted and killed in large numbers until its protected status. Farmers still kill birds. The main threat to this species is predation by introduced mammals- stoats (Mustela erminea), brush-tailed possums (Trichosurus vulpecula) and cats (Felis catus) (BirdLife International 2008).
Threat to endangered species: Predation by stoats is an important factor in the loss of native bird populations. Observations show that stoats kill kiwi chicks, Apteryx spp. under 1000 g, averaging 94% a year when uncontrolled (McLennan et al. 1996), (see Apteryx australis; Apteryx haastii; Apteryx mantelli in IUCN Red List of Threatened Species). Stoat predation on kaka nestlings and adults, in particular females incubating eggs have caused a highly skewed sex ratio and declines in kaka populations and local extinctions (see Nestor meridionalis in IUCN Red List of Threatened Species). Stoats have also been known to raid nests of vulnerable birds especially those that use tree-holes, eg mohua (see Mohoua ochrocephala in IUCN Red List of Threatened Species), stoats are known to predate on mohua eggs, chicks and a disproportionate number of adult females, during the years this happens adult female proportions in some populations can decrease by 50 to 100%. Stoat predation also threatens birds that nest on the ground, eg the threatened shorebird, the New Zealand dotterel (see Charadrius obscurus in IUCN Red List of Threatened Species) (Elliott, 1996; Elliott, et al. 1996; Dowding and Murphy, 1996; Wilson et al., 1998; Dowding and Murphy 2001; Moorhouse et al. 2003).
South Island (New Zealand)
Threat to endangered species: The South Island Wren (see Xenicus gilviventris in IUCN Red List of Threatened Species) is endemic to New Zealand. Once found in the North Island prior to European settlement, it is now restricted to the South Island, where it ranges from north-west Nelson, down through Westland and the Southern Alps, to Fiordland. The major threat to this species is predation by introduced mammals, house mouse Mus musculus and stoat, particularly in years when stoat populations are high in response to mouse plagues. The only study on nesting in this species showed significant levels of egg and chick loss to mice and stoat (BirdLife International 2007).