Monitoring avian populations over both the reproductive and non-reproductive seasons is required to better understand population changes. Obtaining baseline data in remote sites, however, is often difficult during the non-breeding season, especially in ice-driven ecosystems. We determined annual changes in numbers of over-wintering sea duck and large-bodied gull species and identified their main areas of concentration at one of the Pribilof Islands (St. Paul) in the Bering Sea. Formally trained local citizens undertook weekly counts using standardized methods over 3 non-breeding seasons (2008–2009; 2009–2010; 2010–2011) from late autumn to early spring. Sea ducks and large-bodied gulls were present nearshore in considerable numbers from November to January, and maximum counts usually occurred between February and March when sea-ice cover is at its maximum near the Pribilof Islands. We found that one-time counts would underestimate some species (Bufflehead, King Eider, Harlequin Duck), their numbers having peaked earlier in the non-breeding season. Across years, Harlequin Duck (47% occurrence; maximum of 476 total individuals at all sites), Long-tailed Duck (23%; maximum of 627) and King Eider (18%; maximum of 136) were the most common and abundant species. Buffleheads (maximum of 24 individuals) and White-winged Scoters (maximum of 500 individuals) were less common (<5% occurrence), and had distinctive localized distributions in intertidal and lagoon habitats. Only Harlequin Ducks and large-bodied gulls varied annually, with nearly twice as many birds in 2011 as in 2008. Large-bodied gull concentrations (maximum of 1230 individuals; primarily Glaucous-winged Gulls) were mostly associated with dockside and outfall fish offal rather than landfill. Given that large-bodied gulls foraged in the same sites and monthly peaks mirrored those of sea ducks, kleptoparasitism is a potential problem, especially in absence of fishery discards. Our study fills a gap in the current understanding of regional waterfowl and large-bodied gull status during the non-breeding season in the Pribilof Islands, an important over-wintering location.
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Vol. 98 • No. 3