Nest Site and Mate Fidelity in a Large Sooty Tern Onychoprion fuscatus Breeding Colony

Many seabird species share characteristics of high inter-annual colony fidelity and prolonged mate fidelity. This study investigates these characteristics in a Sooty Tern Onychoprion fuscatus breeding colony. During the 2021 breeding season, both members of 80 pairs of incubating Sooty Terns were individually ringed in a large breeding colony on Bird Island, Seychelles. Ten pairs were ringed in each of eight identifiable locations within the nesting area. In the 2022 and 2023 breeding seasons, ringed birds were searched for throughout the colony and caught for identification. Their nest sites were marked and their mates were subsequently caught, then identified or ringed. In the two years of study, many birds retained approximate nests sites between years; when birds did change, alterations in colony vegetation could have been responsible. The extent of nest site change between years was likely underestimated, however, due to reduced search effort available in 2023. Between year mate changes suggested that many Bird Island Sooty Terns did not maintain long-term pair bonds and the causes and implications of this are discussed.