Foraging Strategies and Niche Dynamics of Coexisting Shorebirds at Stopover Sites in the Southern Great Plains

Abstract

AbstractShorebirds encounter variable and unpredictable food resources at stopover sites during migration through interior North America. We studied foraging strategies and niche dynamics of American Avocets (Recurvirostra americana), Long-billed Dowitchers (Limnodromus scolopaceus), Least Sandpipers (Calidris minutilla), and Western Sandpipers (C. mauri) at stopover sites in 60 playa lakes of the southern Great Plains. Those species were selected because they are common in our study area during migration and represent a wide range of morphological classes. Overall foraging niches (linear combination of diet diversity, prey size, foraging-method diversity, and water depth) of avocets and dowitchers were segregated from each other and from Least and Western sandpipers. Overall foraging niches of Least and Western sandpipers were similar. Examination of single niche dimensions showed that avocets and dowitchers consumed larger prey and foraged in deeper water than did Least and Western sandpipers. Within the range of prey sizes consumed by the four individual species, all species selected small prey (0.1–5.0 mm). Preference of relatively small prey by avocets and dowitchers was likely a function of small prey being more abundant in playas than large prey (>10 mm). However, selection of small prey by Least and Western sandpipers was likely a function of lower handling costs associated with small prey. Abundance of prey items in diets of each species was not correlated with nutritional and energetic quality of prey items, but abundance of prey in the diet was correlated with abundance of prey in playa lakes. That suggests that all four shorebird species adopt an opportunistic foraging strategy during migration. Use of opportunism is likely critical for shorebirds to continue migration and arrive on breeding grounds in good condition.