Ecology of spring and fall migrant shorebirds in the Playa Lakes Region of Texas

During spring and summer/fall migration, shorebirds rely on stopover areas to replenish energy reserves and fulflll nutrient requirements. Playas in the Playa Lakes Region (PLR) of west Texas may provide critical stopover habitats for migrant shorebirds. My study documented species compositions, migration chronologies, and use of habitat of migrant shorebirds in the PLR. Furthermore, I examined behavioral ecology, feeding ecology, and niche segregation of American avocet, long-billed dowitcher, least sandpiper, and western sandpiper.;I observed 30 different shorebird species using playas. The dominant species during spring were avocets, dowitchers, and Wilson's phalaropes, while the dominant species during summer/fall were avocets, dowitchers, long-billed curlews, and stilt sandpipers. Migration chronologies were distinct in spring and protracted in summer/fall. Shorebirds tended to use playas that contained sparse vegetation (;Time-activity budgets of the 4 species revealed that feeding was the most important activity for least and western sandpipers during both migrational periods, while feeding and sleeping/resting were important activities for dowitchers and avocets. This indicates that migrant shorebirds use playas to replenish energy and nutrient reserves.;Invertebrates were an important component in the diets of avocets, dowitchers, least sandpipers, and western sandpipers. During spring, chironomids were the predominant invertebrate in the diets of all 4 species. The diets of all 4 species were more diverse in summer/fall. Shorebird foraging activities appeared to have a minimal impact on invertebrate populations.;Niche space differed among large species (avocet), medium species (dowitcher) and small species (least and western sandpipers). The foraging habitat dimension appeared to be the most important resource dimension for segregating the species. Because least and western sandpipers occupied similar niche spaces, a temporal niche dimension may be important in segregating them.;Foraging strategies of all 4 species appeared to be opportunistic. Avocets and dowitchers opportunistically consumed prey sizes relative to prey size availability, while least and western sandpipers were opportunists on small-prey items. The opportunistic approaches of the 4 species is likely a response to the variable and unpredictable food resources they encounter at stopover sites.