Incubation behavior of king eiders on the coastal plain of northern Alaska

Incubating birds balance their energetic demands during incubation with the needs of the developing embryos. Incubation behavior is correlated with body size; larger birds can accumulate more endogenous reserves and maintain higher incubation constancy. King eiders (Somateria spectabilis) contend with variable and cold spring weather, little nesting cover, and low food availability, and thus are likely to rely heavily on endogenous reserves to maintain high incubation constancy. We examined the patterns of nest attendance of king eiders at Teshekpuk and Kuparuk, Alaska (2002-2005) in relation to clutch size, daily temperature, and endogenous reserves to explore factors controlling incubation behavior. Females at Kuparuk had higher constancy (98.5 +/- A 0.2%, n = 30) than at Teshekpuk (96.9 +/- A 0.8%, n = 26), largely due to length of recesses. Mean recess length ranged from 21.5 to 23.7 min at Kuparuk, and from 28.5 to 51.2 min at Teshekpuk. Mean body mass on arrival at breeding grounds (range; Teshekpuk 1,541-1,805, Kuparuk 1,616-1,760), and at the end of incubation (Teshekpuk 1,113-1,174, Kuparuk 1,173-1,183), did not vary between sites or among years (F < 1.1, P > 0.3). Daily constancy increased 1% with every 5A degrees C increase in minimum daily temperature (beta (min) = 0.005, 95% CI 0.002, 0.009). Higher constancy combined with similar mass loss at Kuparuk implies that females there met foraging requirements with shorter recesses. Additionally, females took more recesses at low temperatures, suggesting increased maintenance needs which were potentially ameliorated by feeding during these recesses, indicating that metabolic costs and local foraging conditions drove incubation behavior.