Spatiotemporal species distribution models of colony census and at-sea survey data for Fratercula cirrhata (Tufted Puffin) and F. corniculata (Horned Puffin) reveal long-term declines in Kodiak, Alaska

Abstract The conservation status of Fratercula cirrhata (Tufted Puffin) in the Gulf of Alaska ecosystem, which supports >30–40% of the global population, remains unclear owing to limited or inconsistent monitoring strategies. With similar challenges and less data, the status of the ecologically similar F. corniculata (Horned Puffin) is even less certain. To address these issues, we compiled and analyzed 2 independent long-term datasets collected in the Kodiak Archipelago, Alaska, USA (56–59°N, 151–155°W): (1) 2,121 counts of puffins attending 322 colonies collected from 1975 to 2021 and (2) at-sea densities from 8,954 ship-based transect samples collected during the breeding season from 1975 to 2022. We compared separate joint species distribution models for each survey data type to estimate abundance and long-term trends of F. cirrhata and F. corniculata. Model estimates suggest that the current population (median ± 95% CI) of F. cirrhata includes 538,435 (± 45.4%) individuals at sea and 92,206 (± 36.4%) individuals at colonies, representing overall log-linear declines of 50% at sea and 88% at colonies since 1975. Current estimates for F. corniculata include 44,790 (± 65.0%) individuals at sea, and 8,165 (± 50.4%) individuals at colonies, representing overall log-linear declines of 22% at sea and 67% at colonies since 1975. Parallel trends derived from at-sea and colony surveys, despite measuring different segments of the population, provide strong evidence that both methods can be used effectively to estimate trends of burrow-nesting puffins. Steep declines of both puffin species in the Gulf of Alaska align with declines of other breeding seabirds and point to climate-driven changes in food supplies as likely factors influencing seabird populations in the region.