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We investigated body-mass dynamics during incubation of Long-tailed Ducks (Clangula hyemalis) nesting in Canada's central Arctic, 1998-2003. Long-tailed Duck females (n = 37) lost 7% of pre-incubation body mass during incubation; on average, females weighed 618 [+ or -] 15 g (mean [+ or -] SE) at clutch completion and 575 [+ or -] 11 g at hatch. Given the differences in body size, Long-tailed Ducks relied less on endogenous reserves than sympatric King Eiders (Somateria spectabilis), but lost less mass than similar-sized waterfowl species nesting in temperate climates. Preliminary data suggest that Long-tailed Ducks maintain similar or higher nest-attendance rates than temperate-nesting waterfowl of similar size, and we suggest that access to locally abundant, high-quality foods enable Long-tailed Duck females to maintain high incubation constancy without sacrificing female body condition. Nevertheless, Long-tailed Ducks appear to differ widely from most Arctic-nesting waterfowl in nutritional strategy for nesting. Received 13 February 2004, accepted 4 October 2004. Key words: body mass, Clangula hyemalis, endogenous reserves, King Eider, Long-tailed Duck, incubation, Somateria spectabilis, Queen Maud Gulf Bird Sanctuary. Nous avons etudie la dynamique de la masse corporelle au cours de l'incubation chez des hareldes kakawi (Clangula hyemalis) nichant dans l'Arctique canadien central entre 1998 et 2003. Les femelles d'Harelde kakawi (n = 37) ont perdu 7% de leur masse corporelle au cours de l'incubation. En moyenne, les femelles pesaient 618 [+ or -] 15 g (moyenne [+ or -] erreur-type) apres avoir complete leur couvee et 575 [+ or -] 11 g a l'eclosion. Etant donne les differences en termes de masse corporelle, l'Harelde kakawi depend moins des reserves endogenes que l'Eider a tete grise (Somateria spectabilis) qui niche en sympatrie, mais perdent moins de poids que d'autres especes de sauvagine de taille similaire nichant dans des climats temperes. Les donnees preliminaires suggerent que l'Harelde kakawi maintient un taux de presence au nid similaire ou plus eleve que les especes de sauvagine de taille similaire nichant dans des climats temperes. Nous suggerons egalement que l'acces a la nourriture localement abondante et de haute qualite permet aux femelles d'Harelde kakawi de maintenir une grande constance d'incubation sans sacrifier leur condition corporelle. Neanmoins, en ce qui concerne la strategie nutritionnelle au moment de l'incubation, l'Harelde kakawi semble differer grandement de la plupart des autres especes de sauvagine nichant dans l'Arctique.

Populations of several species of North American sea ducks have declined in the past few decades. Exposure to environmental contaminants, particularly metals, has been proposed as one of many possible factors contributing to these declines. Population dynamics are influenced by survival rates and breeding effort. In the present study, we examined the relationships between blood metal concentrations (Cd, Pb, Se, and Hg) and apparent annual survival and recapture probabilities (the latter as a surrogate for breeding effort) in adult females of two sea duck species, the king eider (Somateria spectabilis) and the white-winged scoter (Melanitta fusca), both of which have experienced declines in continental population during in recent years. No support was found for the hypothesis that exposure of white-winged scoters to these metals or of king eiders to Cd, Se, and Pb adversely affected probabilities of apparent annual survival. We detected a weak negative relationship (... = -0.833) between Hg and annual survival of king eiders, but the 90% confidence interval of the slope estimate overlapped zero (-2.439 to +0.672). Recapture probabilities were unrelated to concentrations of Cd, Se, and Pb in either species. Evidence indicated that Hg concentrations affected recapture probability in white-winged scoters (... = -194.77; 90% confidence interval, -203.770 to -185.778). Mercury levels were low in both species, and blood samples may not adequately represent long-term exposure to Hg. Therefore, conclusions regarding Hg effects on these birds should be considered with caution. [ABSTRACT FROM AUTHOR]