Nestboxes augment seabird breeding performance in a high-density colony: insight from 15 years of monitoring data.
1. The provision of artificial nest structures is used in the conservation of a broad range of bird groups including raptors, owls, ducks, passerines and seabirds, with varying degrees of success. 2. Artificial nestboxes have been provided to increase the density and breeding success of Roseate Tern pairs at colonies in north-west Europe and the eastern seaboard of the USA and Canada, but their effect on breeding productivity has never been comprehensively quantified. 3. Using 15 years of monitoring data, based on daily nest monitoring visits, we carried out a comparative analysis of the breeding performance of Roseate Tern pairs utilizing artificial nestboxes with those in open nests, on Rockabill Island (Ireland), to evaluate the effectiveness of nestbox installation as a conservation measure. 4. Nestboxes were used ahead of open sites early in the season, likely by the experienced breeding pairs. Hatching success and fledging success were higher for pairs in nestboxes compared with those in open nest sites. Earlier clutches were more successful than later ones, independent of the effects of nest site type. 5. The results of this study show definitively that Roseate Terns nesting in nestboxes perform better than those using open nest sites at their largest European colony and that nestboxes are chosen ahead of other sites, likely by the experienced breeding pairs. We recommend the continued and expanded use of nestboxes to help maximize the densities and breeding performance of the Roseate Tern.