Feeding ecology and behavior of postbreeding male Blue-winged Teal and Northern Shovelers

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Abstract
This study examined foraging strategies in male Northern Shovelers (Anas clypeata) and Blue-winged Teal (Anas discors). Differences in time–activity budgets and esophageal contents between the two species indicated major differences in the degree of foraging specialization. Preflightless male Northern Shovelers spent 84.2% of time foraging, with dabbling in the water column as the principal foraging mode (83.4%), while postflightless male shovelers spent 81.6% of time foraging (78.7% dabbling). Preflightless male Blue-winged Teal spent 68.6% of time foraging, with dabbling in mud (32.5%) and picking in vegetation (29.4%) as the two principal modes, whereas postflightless male bluewings spent 85.9% of time foraging (dabbling in mud 40.6%, and picking 34.2%). Most male Northern Shoveler food items were cladocerans (85.5%) or chironomid pupae (12.9%); this was related to the specialized foraging method employed by shovelers. Male Blue-winged Teal food items were principally gastropods (44.3%), culicids (29.2%), seeds and vegetation (15.5%), and chironomids (5.6%), which corresponded to the plastic feeding behaviors of bluewings. Examination of esophageal items revealed that male Northern Shovelers did little feeding during the summer flightless period, while male Blue-winged Teal fed throughout the period.