Do nest boxes breed the target species or its competitors? A case study of a critically endangered bird

Nest boxes are widely used for habitat restoration. Unfortunately, competitors of the target species may exploit nest boxes, creating perverse outcomes. Avoiding habitats preferred by nontarget species, while favoring those of the target species, requires an adaptive management approach if limited information about species preferences is available when deploying boxes. Using nest boxes intended for Swift Parrots Lathamus discolor, we identify factors associated with nontarget species occupancy (Common Starling Sturnus vulgaris and Tree Martin Petrochelidon nigricans) in newly deployed boxes in 2016, and then again after 3 years had elapsed in 2019. Box occupancy by different species depended on the interaction between distance of individual boxes to the forest edge and year. Although the target species exploited similar numbers of nest boxes in both years, competitors were the main beneficiaries of established boxes. A subordinate native nest competitor increased box occupancy likelihood at greater distances from forest edges in both years, but the relationship was stronger in 2019. Introduced Common Starlings S. vulgaris were most likely to occupy boxes close to forest edges, but the magnitude of this relationship was much greater for established than newly deployed boxes. We suggest that permanent box deployments for Swift Parrots may produce perverse outcomes by increasing nesting habitat for Common Starlings. We suggest that for species that only use cavities for part of their life cycle, managers should limit access to boxes outside of critical times to reduce the likelihood that pest populations can exploit restoration efforts and create new problems.