Trial reintroduction of buff weka to an unfenced mainland site in central South Island,New Zealand

While there have been significant conservation successes through restoration of island biodiversity following the eradication of invasive predators, a major challenge remains to reintroduce native species within larger mainland systems that support suites of introduced mammalian predators. Strategies to enhance establishment and persistence of reintroduced populations include pre‐release management to reduce post‐release dispersal, and habitat restoration such as predator control at release sites. Evaluation of such strategies critically requires strategic and intensive post‐release monitoring to identify drivers of success or the specific causes of failures. The buff weka (Gallirallus australis hectori), a flightless rail, was reintroduced to an unfenced mainland island on New Zealand's South. Past reintroductions on the mainland have all failed, but lack of post‐release monitoring has meant the exact cause and timing of failures is unknown. We investigate the ability of buff weka to establish a mainland population in conjunction with high intensity predator control. Nineteen buff weka (15 males, 4 females) were transferred from predator‐free islands in Lake Wakatipu, South Island, to Motatapu Station and held in a pre‐release enclosure for 6 weeks. Using a combination of very high frequency (VHF) and Global Positioning System (GPS) telemetry, released birds were monitored every 2 days for 4 months post‐release. Following release, no buff weka dispersed off Motatapu Station. Survival, however, was low and by the end of the study, 12 (63%) buff weka had been predated by introduced mustelids, ferrets (Mustela furo) and stoats (Mustela erminea). The lack of dispersal by buff weka suggests the presence of favourable resources on Motatapu Station. However, the low survival rate indicates that the predator‐trapping network was insufficient to suppress predator numbers to a level low enough for buff weka population persistence.