Domestic cats have a cosmopolitan distribution, commonly residing in urban, suburban and peri-urban environments that are also critical for biodiversity conservation. This study describes the impact of a desexed, free-roaming cat on the behavior of a threatened coastal seabird, the Australian Fairy Tern, Sternula nereis nereis, in Mandurah, south-western Australia. Wildlife cameras and direct observations of cat incursions into the tern colony at night, decapitated carcasses of adult terns, dead, injured or missing tern chicks, and cat tracks and scats around the colony provided strong evidence of cat predation, which led to an initial change in nesting behavior and, ultimately, colony abandonment and the reproductive failure of 111 nests. The death of six breeding terns from the population was a considerable loss for this threatened species and had the potential to limit population growth. This study highlights the significant negative impacts of free-roaming cats on wildlife and the need for monitoring and controlling cats at sites managed for species conservation. It also provides strong evidence against the practice of trap-neuter-release programs and demonstrates that desexed cats can continue to negatively impact wildlife post-release directly through predation, but also indirectly through fundamental changes in prey behavior and a reduction in parental care.

The Australian fairy tern metapopulation in Western Australian is distributed over an extensive stretch of coastline (≤2500 km). Using mark–recapture and coordinated community-based resightings of marked birds, this study reveals important insights into the seasonal movement, interchange and key locations used by Australian fairy terns. The Western Australian metapopulation consists of a widely distributed, partially migratory spring/summer-breeding population and a smaller, winter-breeding, sedentary population on the Pilbara coast. The spring/summer-breeding population winters, primarily, around the northern islands of the Houtman Abrolhos, before migrating to breeding areas as far south as Point Malcolm on the eastern south coast and as far north as the Ningaloo coast (Exmouth). Thus, in Western Australia, Australian fairy terns from the same population reproduce in both tropical and temperate marine regions. Associations between birds, persisting over multiple seasons, suggest that group adherence may be an important behavioural trait of these small terns. Based on the recent use of breeding sites and the likely spatial extent of exchange of breeding adults and natal recruits, seven ‘neighbourhoods’ are proposed, which likely represent the best units to underpin a conservation strategy for this threatened coastal seabird. The combination of small population size, strong area fidelity and the potential for strong group adherence among individuals are important considerations for the development of effective conservation strategies in Western Australia. Maintaining the Australian fairy tern population size within the suggested management units is critical for the long-term conservation of this species.

This research describes the breeding ecology, behaviour and substrate preferences of the Australian Fairy Tern, Sternula nereis nereis, in four colonies around Perth, Western Australia between 2018 and 2020. Extensive field observations, supported by a bird banding study and sunrise to sunset video recording were used at colony and roosting sites to determine the processes of mating, colony formation, egg-laying and incubation periods, post-hatching care and breeding success (fledglings per pair). At a colony in North Fremantle, the median nest spacing was 0.71 m (mean ± s.e. = 0.89 ± 0.05 m), which increased over time. Birds establishing nests within a week of the first eggs being laid selected sites with significantly higher percentage beach shell cover (73.5 ± 4.5%) than those laying later in the season (58.2 ± 7.9%) and on average, birds selected sites with higher shell cover (64.9 ± 2.8%, n = 114) than a random sample of sites within the colony (53.7 ± 4.4%, n = 44). Incubation periods ranged from 17 to 26 days (n = 86, mean = 21 ± 0.17 days). Incubation shift duration was highly variable, with both sexes contributing, almost equally to the care of the brood (mean = 1.27 ± 6.11 h). Chicks fledged 21–23 (mean = 22 ± 0.21, n = 10) days following hatching, with all banded juveniles leaving the colony site within 8 days of fledgling. The information gained from this research helps inform conservation strategies for this vulnerable species, where management interventions are frequently necessary to prevent population decline.