In many waterfowl species, females in better body condition have greater reproductive success than those in poor condition; thus, large-scale changes in body condition could influence species' population dynamics. Indices of annual productivity have decreased in Lesser Scaup (Aythya affinis), and the "spring condition" hypothesis (SCH) has been proposed to account for poor production and low populations in this species. We compared nutrient reserves of female Lesser Scaup and Ring-necked Ducks (A. collaris) collected during the breeding season at multiple sites in the Canadian boreal forest, the region where ~70% of both species breed and where they have had contrasting population trends for the past 25 years. Lesser Scaup tended to carry greater somatic lipid but slightly lower protein reserves than Ring-necked Ducks, after controlling for size. The proportion of females developing follicles was similar in both species, though Lesser Scaup initiated egg development later and exhibited less temporal variance in nesting date than Ring-necked Ducks. We also directly tested the SCH by comparing contemporary arrival and prebreeding body masses of Lesser Scaup with historical values at one boreal-forest site. However, body masses of Lesser Scaup collected in 2003–2004 were comparable to those of Lesser Scaup collected at Yellowknife, Northwest Territories, during 1968–1970. Overall, our results suggest that currently, body condition of boreal-breeding Lesser Scaup is relatively similar to that of Ring-necked Ducks and to historical levels for Lesser Scaup. Future studies of factors that limit recovery of Lesser Scaup should examine migration patterns and the effects of climate change on the timing of both energetic requirements in Lesser Scaup and food-resource availability.
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Vol. 125 • No. 2