POPULATION INDICES, TRENDS, AND DISTRIBUTION OF BREEDING WATERBIRDS ON THE ARCTIC COASTAL PLAIN, ALASKA, 2007-2024

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 and Steller’s eiders, yellow-billed loons, and snow geese. This report focuses on results from the 2018-2024 ACP surveys and presents population indices for all species from 2007-2024. No surveys were conducted in 2020-2021 due to the COVID pandemic. For surveys flown in 2018, 2019, 2022-2024, the respective indicated total bird indices and their associated 95% confidence intervals (CI) for spectacled eiders were 4,745 (3,212 -6,277), 3,738 (2,820 -4,656), 2,335 (1,556 -3,115), 2,284 (1,494 -3,074), and 2,008 (1,138 -2,878); and for Steller’s eiders were 95 (0 -300), 167 (14 -320), 188 (0 -468), 96 (0 -276), 286 (0 -577). Long-term (2007-2024) mean annual population indices and trends (and their associated 95% CIs) for these species and others of conservation concern, were as follows: spectacled eiders (indicated total birds) 5,012 (3,661 -6,362), growth rate 0.93 (0.90 -0.97); Steller’s eiders (indicated total birds) 169 (0 -466), growth rate
1.05 (0.75 -1.44); yellow-billed loons (total birds) 2,120 (1,580 -2,660), growth rate 1.00 (0.95 -1.05); and snow geese (total birds) 41,814 (1,051 -82,576), growth rate 1.12 (1.00 -1.25). Our population indices do not account for incomplete detection or other sources of bias at this time, although the model we used to estimate growth rate removes average observer effects. Posterior probabilities for a long-term (2007–2024) growth rate < 1.00 were > 0.975 for scaup, spectacled eiders, king eiders, and jaeger species, indicating high confidence in long-term population declines for these species. By the same metrics, posterior probabilities for population increase were ≥ 0.90 for snow geese and sandhill cranes, indicating moderate confidence in long-term population increases for these species, while mallards and common ravens showed moderate confidence for decreasing trends (> 0.90 posterior probability of decrease). Growth rates for greater white-fronted geese and tundra swans indicated relatively stable populations (95% credible interval bounds for long-term growth rate were ± 3% of a long-term growth rate of 1.00), although the posterior probability of a decrease for tundra swans was 0.91, indicating moderate confidence in a slow decrease for that species. Confidence in directional trends for all other species was more limited (< 0.90 posterior probability for decrease or < 0.80 for increase).