Evaluating the dispersal of a translocated kakaruai (South Island robin; Petroica australis) population out of Orokonui Ecosanctuary

Fenced ecosanctuaries provide critical refuges for native species vulnerable to predation and have driven major biodiversity gains. Understanding whether they can also support sustainable populations beyond their boundaries is an important next step. While previous studies have documented native species dispersing beyond ecosanctuaries, few have utilised methods that explicitly quantify dispersal and the establishment of resident birds. We quantified dispersal of a kakaruai | South Island robin (Petroica australis) population, translocated to Orokonui Ecosanctuary in 2010, by evaluating site occupancy, persistence in previously colonised areas, and establishment of new territories within a site. Surveys were conducted during the kakaruai breeding season in 2018, 2019, and 2022. In 2018, five fixed transects were each surveyed twice. This was expanded to 11 transects in 2019 and 2022. Between 2018 and 2022, the number of sites occupied by kakaruai steadily increased, with four new sites colonised in the final survey year. Three sites showed persistent occupancy over multiple years, and both the number of individual birds and the number of territories within established sites increased over time, possibly as individuals settled near conspecifics. Data from 2019 and 2022 were then used to generate a model-averaged analysis incorporating site, year, connectivity, and habitat type (native or mixed) as key predictors of kakaruai presence. The strongest predictor of kakaruai presence was proximity to the ecosanctuary, with presence declining significantly beyond 1500 metres. Our research provides a valuable model for assessing initial dispersal success at the population level by using species-specific monitoring approaches rather than general bird counts. Demonstrating dispersal beyond the fence is a critical first step toward extending the ecological benefits of sanctuaries into the wider landscape, informing strategies that enhance connectivity and long-term population viability.