Drivers of colony failure in a vulnerable coastal seabird, the Australian Fairy Tern (Sternula nereis nereis)

Abstract

Context. Understanding breeding success and site threat profiles is critical to conservation planning, particularly for species of conservation concern. Regular surveillance is fundamental to observing spatiotemporal changes at breeding colonies. Still, it can be challenging for species with broadly distributed, unpredictable populations susceptible to various threats. In these cases, cooperative networks and citizen science programs offer an opportunity to support monitoring and conservation efforts. Aims. This study aimed to assess the outcomes, threats and sources of breeding failure at Australian Fairy Tern (Sternula nereis nereis) colonies. Methods. Through collaborative surveillance, this study identified the outcomes and threats at 77 monitored colonies over five breeding seasons between 2017/18 and 2021/22. The leading causes of nest failure were then considered against the Recovery Plan for the Australian Fairy Tern to understand how the observed threats compare with the identified risks in this plan. Key results. Nearly half (48%) of all colonies failed, with predation (32%) and inundation (27%) being the biggest causes of failure. At least 10 native and four invasive/domestic species contributed to the mortality of eggs, chicks, and/or adults or complete colony failure. Disturbance, including off-road vehicles, was identified as a recurring threat, impacting at least 30% of colonies. Conclusions. These identified threats have the potential to drive populationlevel effects and were consistent with those identified under the Recovery Plan. Implications. This study highlights the importance of developing practical solutions, including habitat protection, the control of invasive species and education programs to safeguard colonies and boost breeding success.