Birds of Oeno Atoll, Pitcairn Islands, in September 2025

The Pitcairn Islands support regionally significant seabird assemblages, yet long gaps in monitoring limit understanding of seabird breeding phenology and basic biology. Observations from Oeno Atoll and Henderson Island in September 2025 reveal the importance of eradicating invasive Polynesian rats (Rattus exulans) in 1997 and habitat structure and highlight the potential for asynchronous breeding in many species. Oeno now supports high breeding activity across multiple trophic and nesting guilds, with widespread evidence of recruitment and large colony sizes relative to pre-eradication estimates. Breeding phenology was often protracted or shifted later than previously reported, highlighting substantial temporal variability both within and among islands. In contrast, ground-nesting species on Henderson continue to experience low reproductive success, consistent with ongoing predation pressure from Polynesian rats. Patterns of absence or low detectability in several taxa further emphasise the challenges of short-duration surveys in systems dominated by asynchronous or subannual breeders. Collectively, these findings underscore Oeno’s importance as a recovering seabird stronghold and highlight the need for repeated, seasonally explicit surveys to resolve phenology, population trends, and ecosystem responses to management interventions.