How low can you sow? House mouse eradication on Motuareronui/Adele Island

House mice (Mus musculus) are highly invasive mammals and can cause extensive ecosystem damage on islands where they are the sole mammalian pest species. Capability to eradicate mice has improved in recent years. Mouse eradication has been achieved on large islands where mice cohabit with other rodents and islands where mice are the sole mammalian pest. As the islands targeted for eradication become larger and more challenging, reduced toxic cereal bait application rates can reduce both complexity and cost, and ultimately make currently unachievable operations feasible. Auckland Island (45 891 ha) in New Zealand’s subantarctic region is a desirable target for mouse eradication. However, logistics at this scale indicate that the required bait volume using New Zealand’s currently agreed best practice (two applications, each 8 kg ha⁻¹) is not feasible using available resources. Small islands provide an opportunity to experiment with eradication methods with acceptable levels of risk. Here we test the eradication of mice from a small island in New Zealand using a low bait application rate. A single application of 3 kg ha⁻¹ of rodent cereal baits containing brodifacoum was aerially applied on Motuareronui/Adele Island (87 ha) in New Zealand’s Abel Tasman National Park, in winter 2017. Intensive monitoring immediately following bait application showed the mouse population rapidly succumbed to the baiting operation. Rodent dog checks 5 months after baiting increased confidence in the operations’ success. A mouse was detected and caught 7 months later in a biosecurity trap network, but genetic analysis determined that this mouse was a recent incursion rather than the result of eradication failure. No further mice were caught, and the eradication was declared a success two summers after baiting. This study shows how undertaking, reporting on, and reviewing appropriate high-standard field trials can contribute to the evolution of best practice. This study adds to a growing body of evidence that low application baiting (relative to best practice) can be considered feasible for mouse eradications on islands where the benefits outweigh the risks, and points to further avenues of research to reduce risk and broaden the application of this method.