Using experimental trials to improve translocation protocols for a cryptic, endangered passerine

Abstract

When key ecological information is lacking, conservation translocations should be conducted within an adaptive, experimental framework to maximise knowledge gained and to increase the probability of success. Here we investigated whether timing of release or composition of release groups influenced indices of success during a trial reintroduction of the mallee emu-wren, Stipiturus mallee, to Ngarkat Conservation Park, South Australia. We translocated cohorts of 40 and 38 birds in the Austral autumn and spring of 2018 respectively. We released individuals in small groups, comprising either familiar or unfamiliar birds, and intensively monitored all treatments for 2 weeks post-release to quantify short-term survival and dispersal. We used occupancy modelling to assess persistence of the translocated population for 2 years following releases. We also monitored source populations to assess the impact of removals. Mallee emu-wrens released in spring were more likely to remain at the release site and attempt breeding. Familiarity within a release group did not influence short-term survival. Mallee emu-wren occupancy at the release sites declined following releases and by July 2019 (12–15 months after release), we could no longer detect any emu-wrens. Density at source populations was lower 12 months after removal compared with pre-harvest levels, though these differences were not significant. Despite the failure to establish a population, we gained valuable management insights regarding both the focal species, and translocation practice more broadly. Timing of release can influence short-term indices of success. Spring releases should be considered priority actions in future mallee emu-wren translocations.