Contrasting trends of Falkland skua populations at two key nesting sites

Abstract The Falkland skua ( Stercorarius antarcticus antarcticus ) is a long-lived seabird breeding primarily in the Falkland Islands. Despite its current Least Concern status by the IUCN, its population is declining, and trends remain poorly understood. We surveyed breeding populations across 18 islands and compared the changes in population size on New Island and Steeple Jason Island, the two largest known nesting sites. Between 2009 and 2023, the New Island population declined by 26% (2.1% annually), from 333 to 246 apparently occupied territories (AOTs). Over a similar period, the Steeple Jason Island population increased by 50% (3.1% annually), from 222 to 332 AOTs - reversing the population sizes at the two sites. A higher proportion of single-egg clutches and empty nests on New Island suggests lower breeding success. In contrast, the growth on Steeple Jason Island may be associated with a high number of food sources, including the establishment of a breeding rookery of South American fur seals ( Arctocephalus australis ). Resightings of skuas ringed as chicks indicate natal philopatry but also some dispersal across the archipelago. These results emphasise the need for a broad, multi-colony approach to better understand and manage Falkland skua populations.