Translocation of Hamilton’s frog, Leiopelma hamiltoni, to a mainland sanctuary occupied by mice Mus musculus

A two-phase translocation of Hamilton's frog (Leiopelma hamiltoni) into Zealandia Ecosanctuary Te Māra a Tāne, in Wellington, was the first attempt to restore the species to the mainland. All non-native mammals had been eradicated there, but house mice (Mus musculus) re-invaded, providing an opportunity to investigate their impact on L. hamiltoni. In Phase I, 60 frogs were translocated into mouse-proof enclosures over 2006–2007. Twelve months into Phase I, 29 surviving frogs were kept in a predator-proof enclosure, and 29 surviving frogs were released into adjacent forest, then monitored over eight months. Survival and recruitment were high in the enclosure, but low in the forest. For Phase II, a further 101 frogs were released in 2012, after a fence had been erected around the release site to exclude little spotted kiwi (Apteryx owenii), a potential predator. In Phase II, frog survival and mouse numbers were monitored over nine months, with mouse density being suppressed by annual poisoning operations. On night surveys, 86 of the 101 released frogs were recaptured in the forest, plus four adults from the Phase I release and twelve of their progeny. Overall survival was 0.914 (0.87–0.94 95% CI), but population estimates indicated a negative trend from the second capture period. Negative binomial generalised linear modelling showed temperature was positively correlated with frog emergence (p < 0.001). Relative humidity approached significance for frog emergence (p = 0.0517), but mouse activity, precipitation during sampling, and precipitation the previous 24 hours did not impact emergence (p > 0.05). Surviving adult and young L. hamiltoni from Phase I demonstrated some capacity for survival in protected mainland areas with invasive mammal control in place. However, further studies are warranted to better determine their longer-term survival in Zealandia and alongside the threat of mice, as well as of avian predators such as kiwi, and more generally of other invasive mammals.