Body condition of spring-migrating Green-winged Teal (Anas crecca)

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Spring migration is an energetically demanding event that can impact nutrient dynamics of individuals during the breeding season through carry-over effects. Limited food availability at spring stopover areas may have cross-seasonal effects that adversely impact waterfowl populations. We collected 161 Green-winged Teal (Anas crecca Linnaeus, 1758; hereafter Teal) throughout the Illinois River Valley, USA, during February–April of 2016–2018 and estimated body condition using three condition indices (scaled mass index, scaled wing index, body-size index) for comparison with carcass lipid and protein values. Lipids were 18.3% (95% CI = 1.0%–38.5%) and 21.6% (95% CI = 4.8%–41.0%) greater at locations with moderate (250–600 kg/ha) and high (>600 kg/ha) moist-soil seed densities, respectively, than low moist-seed density (<250 kg/ha) sites. Lipids also increased 2.4% (95% CI = 0.2%–5.1%) with every 10% increase in the proportion of plant seeds in diets and decreased 0.9% (SE = 0.4%–1.4%) and 3.8% (SE = 2.1%–5.4%) with every 1-day increase in collection date and 1 °C rise in mean temperature, respectively. Condition indices based on morphology were poor (r ≤ 0.45) predictors of lipids and led to potentially erroneous conclusions regarding important contributions to body condition. Availability of emergent wetlands with adequate food resources may affect lipid reserves of Teal during spring migration and have cross-seasonal effects during the breeding season.