POPULATION INDICES, TRENDS, AND DISTRIBUTION OF BREEDING WATERBIRDS ON THE ARCTIC COASTAL PLAIN, ALASKA, 2007-2025

The Arctic Coastal Plain Aerial Breeding Population Survey (ACP Survey) provides data on the distribution and relative abundance of 33 bird species (including 29 waterbird species) that nest in northern Alaska. Among those reported are species of conservation concern, including threatened spectacled (Somateria fscheri) and Steller’s eiders (Polysticta stelleri), yellow-billed loons (Gavia adamsii), and snow geese (Anser caerulescens). This report focuses on results from the 2007-2025 ACP surveys and presents population indices for all species from 2007-2025. No surveys were conducted in 2020-2021 due to the COVID pandemic. In 2025, the respective indicated total bird indices and their associated standard errors (SE) for spectacled eiders were 3,280 (SE: 495), and for Steller’s eiders were 191 (SE: 122), while total bird indices for yellow-billed loons were 1,597 (SE: 253), and for snow geese were 171,831 (SE: 56,444). Long-term (2007-2025) mean annual population indices and geometric mean growth rates (with their associated SE or 95% credible intervals in parentheses) for these species were: spectacled eiders (indicated total birds) 4,910 (SE: 679), growth rate 0.94 (0.92 -0.98); Steller’s eiders (indicated total birds) 171 (SE: 150), growth rate 1.02 (0.76 -1.38); yellow-billed loons (total birds) 2,090 (SE: 274), growth rate 0.99 (0.95 -1.03); and snow geese (total birds) 49,462 (SE: 24,382), growth rate 1.13 (1.02 -1.23). Currently, our population indices do not account for incomplete detection or other sources of bias, although the model we used to estimate growth rate removes average observer effects. Our growth rate model indicated long-term (2007-2025) population decline for scaup (Aythya marila and A. affnis), spectacled eiders, king eiders (Somateria spectabilis), and jaeger species (Stercorarius sp.) with posterior probabilites > 0.975, while snow geese showed a high probability (> 0.975) of long-term population increase (up to 23% per year). Greater white-fronted geese (Anser albifrons), northern pintail (Anas acuta), long-tailed ducks (Clangula hyemalis), and Pacifc (Gavia pacifca) and yellow-billed loons were relatively stable, with a posterior mean growth rate between 0.99 and 1.01 (95% CI bound to ≤ 5% increase or decrease). Posterior estimates for other species showed less evidence of long-term population change.