North American scoter populations have declined by approximately 60% over the last 30-50 years. Prior studies of other sea duck species suggest that trace elements can have deleterious effects on overall body condition. For surf scoters (Melanitta perspicillatta) and white-winged scoters (Melanitta fusca), this study tested the following hypotheses: (1) Trace element accumulation differs among seasons, locations, and species; (2) Increased trace elements in tissues correlate with declines in body condition; (3) Surf scoters that shift their feeding to a higher trophic level in spring bioaccumulate higher levels of trace elements; and (4) Selenium and mercury co-accumulate in a 1:1 molar ratio. To test these hypotheses, cadmium (Cd), mercury (Hg), and selenium (Se) in livers and kidneys were collected from adult male surf scoters and white-winged scoters in December 2005 and March 2006 from three locations in Puget Sound, Washington. Trace elements in surf scoters differed among locations, and seasons. Se and Cd in liver and kidney explained 21% of the variance in a matrix of body condition factors in surf scoters. In white-winged scoters, body condition differed between March and December, but trace elements in tissues did not, indicating that contaminants did not explain changes in condition. Thus, hypotheses 1 and 2 received partial support while hypothesis 3 did not. Finally, Se and Hg did not covary in either the kidney or liver of either species (hypothesis 4). Compared to other marine birds, scoters in this study contained low contaminant levels. Nonetheless, inorganic contaminants explained substantial variation in body condition of surf scoters, and potentially contribute to their population declines. These findings suggest that inorganic contaminants, particularly Cd, should be considered in assessing habitat quality for sea ducks.

North American populations of white-winged scoters (<i>Melanitta fusca deglandi</i>) have declined markedly over the past several decades. The causes for decline are uncertain, but likely involve a complexity of events occurring on wintering and breeding areas. To gain insight into potential cross-seasonal effects, I delineated Atlantic and Pacific wintering scoter populations and linked them to a shared breeding area using stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) ratios in feathers. By applying this methodology to a marked breeding population at Redberry Lake, Saskatchewan, I assigned females to putative wintering areas and determined: (1) population structure; (2) the extent of winter site philopatry; and, (3) differences in vital rates and other variates in relation to winter origin. Discriminant function analysis of isotopic ratios in feather samples from known wintering locations resulted in classification probabilities of 96% (<i>n</i> = 149) for Pacific and 78% (<i>n</i> = 32) for Atlantic wintering scoters. Using this methodology, I determined that the Redberry Lake breeding population is comprised of approximately 75% Pacific and 25% Atlantic wintering birds, and its members exhibit high degrees of winter region philopatry based on the classification of successive recaptures over three field seasons. Annual variations in population structure, as well as differences in nest initiation dates and blood contaminant loads in relation to winter area suggest seasonal interactions may influence survival and reproductive success of this population. To gain insight into potential seasonal interactions, I examined nest success and female survival in relation to winter area. No significant differences in nest success in relation to winter area were found, but nests that failed before mid-incubation were not sampled. Adult female survival rate for 2000-2004 was estimated as 0.85, with no significant difference detected between wintering areas. This study demonstrated that it is important to link breeding and wintering areas to better understand the factors influencing population dynamics and to effectively address conservation issues.

North American populations of white-winged scoters (<i>Melanitta fusca deglandi</i>) have declined markedly over the past several decades. The causes for decline are uncertain, but likely involve a complexity of events occurring on wintering and breeding areas. To gain insight into potential cross-seasonal effects, I delineated Atlantic and Pacific wintering scoter populations and linked them to a shared breeding area using stable isotope analysis of carbon (δ13C) and nitrogen (δ15N) ratios in feathers. By applying this methodology to a marked breeding population at Redberry Lake, Saskatchewan, I assigned females to putative wintering areas and determined: (1) population structure; (2) the extent of winter site philopatry; and, (3) differences in vital rates and other variates in relation to winter origin. Discriminant function analysis of isotopic ratios in feather samples from known wintering locations resulted in classification probabilities of 96% (<i>n</i> = 149) for Pacific and 78% (<i>n</i> = 32) for Atlantic wintering scoters. Using this methodology, I determined that the Redberry Lake breeding population is comprised of approximately 75% Pacific and 25% Atlantic wintering birds, and its members exhibit high degrees of winter region philopatry based on the classification of successive recaptures over three field seasons. Annual variations in population structure, as well as differences in nest initiation dates and blood contaminant loads in relation to winter area suggest seasonal interactions may influence survival and reproductive success of this population. To gain insight into potential seasonal interactions, I examined nest success and female survival in relation to winter area. No significant differences in nest success in relation to winter area were found, but nests that failed before mid-incubation were not sampled. Adult female survival rate for 2000-2004 was estimated as 0.85, with no significant difference detected between wintering areas. This study demonstrated that it is important to link breeding and wintering areas to better understand the factors influencing population dynamics and to effectively address conservation issues.