Foraging strategies and niche dynamics of coexisting shorebirds at stopover sites in the southern Great Plains

Shorebirds 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 Dowitchcrs (Limnodroms scolopaceus scolopaceus), Least Sandpi pers (Calidris minutilla), and Western Sandpipers (C.)mauri) at stopover si tes in 60 playa lakes of the southern Great Plains. Those species were sele cted because they are common in our study area during migration and represe nt a wide range of morphological classes. Overall foraging niches (linear c ombination of diet diversity, prey size, foraging-method diversity, and wat er depth) of avocets and dowitchers were segregated from each other and fro m Least and Western sandpipers. Overall foraging niches of Least and Wester n sandpipers were similar. Examination of single niche dimensions showed th at avocets and dowitchers consumed larger prey and foraged in deeper water than did Least and Western sandpipers. Within the range of prey sizes consu med 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 li kely a function of small prey being more abundant in playas than large prey (> 10 mm). However, selection of small prey by Least and Western sandpiper s 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 nu tritional and energetic quality of prey items, but abundance of prey in the diet was correlated with abundance of prey in playa lakes. That suggests t hat all four shorebird species adopt an opportunistic foraging strategy dur ing migration. Use of opportunism is likely critical for shorebirds to cont inue migration and arrive on breeding grounds in good condition.