New Zealand

The impacts of house mice (Mus musculus), one of four invasive rodent species in New Zealand, are only clearly revealed on islands and fenced sanctuaries without rats and other invasive predators which suppress mouse populations, influence their behaviour, and confound their impacts. When the sole invasive mammal on islands, mice can reach high densities and influence ecosystems in similar ways to rats.

Following the incursion of rats (Rattus rattus) on Taukihepa (Big South Cape Island; 93.9 km²) off southern New Zealand in 1963, and the subsequent extirpation of several endemic species, the New Zealand Wildlife Service realised that, contrary to general belief at the time, introduced predators do not reach a natural balance with native species and that a safe breeding habitat for an increasing number of ‘at risk’ species was urgently needed.

In winter 2016, the New Zealand Department of Conservation (DOC) eradicated mice (Mus musculus) from the Antipodes Islands located at 49°S 178°E, 760 km south-east of New Zealand’s South Island. Mice were the only mammalian pest species present. They have extensively impacted the abundance and survival of invertebrates, with likely secondary impacts on endemic terrestrial birds and nesting seabird fauna. Public-private partnerships with DOC instigated the project and provided essential financial support.

Big South Cape Island (Taukihepa) is a 1040 ha island, 1.5 km from the southwest coast of Stewart Island/Rakiura, New Zealand. This island was rat-free until the incursion of ship rats (Rattus rattus) in, or shortly before, 1963, suspected to have been accidentally introduced via local fishing boats that moored at the island with ropes to the shore, and were used to transport the mutton birders to the island.

In locations with a high potential for re-invasion, such as inshore islands, sustained control of invasive species is as important as the initial knock-down for the long-term recovery of native populations. However, ongoing trap maintenance and lure replenishment are barriers to minimising the time and financial costs of long-term suppression, even when automatic traps are used.

Since 1987, I have assisted the Cook Islands Conservation/Environment Service and, more recently, the Takitumu Conservation Area Project and the Avifauna Conservation Programme of the South Pacific Regional Environment Programme (SPREP) to plan and implement a recovery programme for the kakerori, a critically endangered forest bird endemic to Rarotonga. In 1989, the kakerori was one of the 10 rarest birds in the world, and classified as 'critically endangered' (Collar et al. 1994) with a population of just 29 birds. I calculated

Although Talon® baits containing brodifacoum have been used successfully in eradicating rats from some of New Zealand’s offshore islands, little is known about any environmental effects of this toxin. We sampled invertebrates, blackbirds, soil, and water at intervals of 2 days to 9 months to determine whether brodifacoum residues were present after aerial distribution of Talon® 20P cereal pellets on Red Mercury Island and after bait-station use of Talon® 50WB wax-coated cereal blocks on Coppermine Island.