Intrinsic and Extrinsic Factors Determining Diving Duck Condition and Habitat Quality during Spring Migration in the Upper Midwest

The Illinois and Mississippi river corridors historically provide critical stopover habitat for spring-migrating diving ducks (Havera 1999). However, recent evidence suggests that wetlands associated with these river systems in the region provide limited seed and invertebrate biomass during spring (Straub et al. 2012). We evaluated habitat quality throughout the upper Midwest during springs 2014–2015 by sampling foods available to diving ducks and examining an index of daily lipid deposition of lethally collected lesser scaup and canvasbacks (DLDs; Anteau and Afton 2008b). We related habitat quality metrics to body condition, determined by proximate analyses, and habitat selection of diving ducks.Additionally, we estimated levels of the stress hormone, corticosterone, and bioaccumulated hepatic elements to describe physiological condition of lesser scaup at Midwest stopover locations. Our data indicate that regional differences in body condition, stress levels, nutrient acquisition, foraging patch selection, and foraging area selection were more important than other factors (e.g., food densities) during spring migration.We observed low food densities, diverse diets, and negative energy balances, suggesting that food may be limited for diving ducks during spring. In particular, lack of evidence for patch and area selection may indicate that diving ducks are often unable to differentiate foraging patches based on energetic value. Additionally, other stressors such as introduced parasites may be an emerging threat to lesser scaup populations and important contributors to the Spring Condition Hypothesis (England 2016).unpublishednot peer reviewedOpe