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

Abstract

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.

Food Selection by Spring-Migrating Green-Winged Teal

“…We used contemporary, unbiased methods to quantify food selection of spring-migrating teal within a migration stopover region in the Midwest, USA. Consistent with the spring dietshift hypothesis (Klimas et al 2020;Hitchcock et al 2021), we hypothesized that teal would select invertebrates within the Illinois River Valley during spring migration. Additionally, we hypothesized that selection of food items would be impacted by wetland to river connectivity due to the influence of floodplain inundation on vegetative communities during the growing season.…”

“…We tested for differences in selection intensity among age, sex, year, migratory period, and wetland connectivity variables. To control for potential differences in body condition during the spring migration period (Klimas et al 2020), we identified the average peak spring migration date (~15 March) for teal in the IRV using eBird data from 2016-2018 and classified collections as early (before 15 March) or late (on or after 15 March; eBird 2019). We categorized wetland connectivity with the main channel of the Illinois River as 1) directly connected or influenced by the Illinois River below flood stage (connected), 2) influenced by the river at or above moderate flood stage (partially connected), and 3) disconnected via surface water and mostly uninfluenced by the Illinois River (isolated; Lemke et al 2017).…”

“…During February-April 2016-2018, we collected teal at wetlands (~40-2000 ha) in the IRV. We identified wetlands where teal were abundant through ground surveillance and spring waterfowl aerial inventory data from the Illinois Natural History Survey (Stafford et al 2007;Klimas et al 2020). Teal were observed foraging for ≥10 minutes to increase the likelihood of ingesta upon dissection and then lethally collected with a shotgun and non-toxic shot (Swanson and Bartonek 1970).…”

“…Availability and accessibility of food resources at spring stopover sites are important factors affecting the condition of many species of waterfowl (Arzel et al 2006;Stafford et al 2014;Klimas et al 2020). Waterfowl use stopover sites to replenish fat reserves for subsequent migratory movements and in preparation for nest initiation upon breeding ground arrival.…”

“…During spring, waterfowl may encounter conditions that limit nutrient uptake such as low food abundances, adverse weather conditions (e.g., ice coverage, cold temperatures), and increased energy expenditures involved with courtship and pair bonding (Anteau and Afton 2009;Straub et al 2012;Janke et al 2019). Inability to acquire sufficient food resources along spring migration routes can negatively influence body condition in some species of waterfowl, and spring habitat resource quality has been linked to subsequent breeding success in some species (i.e., crossseasonal effects; Sedinger and Alisauskas 2014; Klimas et al 2020). Some waterfowl that reach the breeding grounds with increased nutrient and lipid reserves can exhibit greater breeding success and recruitment (Devries et al 2008).…”