Exploring the variation in spoonbill chick diet and trophic niches between traditional and recently colonised sites in Portugal

Abstract

The Eurasian Spoonbill Platalea leucorodia is currently experiencing an increasing population trend in Western Europe and colonising areas in its breeding range. In this study we assessed the diet and trophic ecology of spoonbill chicks in Portuguese colonies (Ria Formosa and Tagus Estuary) occupied at different years during the population expansion in the country. We accomplished this by combining diet analysis with blood and feather stable isotopic analysis. Spoonbills from the Portuguese colonies relied mainly (but not exclusively) on crustaceans (Ria Formosa = 75%, Tagus Estuary = 72.5%) and fish (Ria Formosa = 17.11%, Tagus Estuary = 37.50%) to feed their chicks. Crustaceans seems to be the most important prey group. Nevertheless, chicks from Ria Formosa were fed with prey from a higher trophic level than chicks from Tagus Estuary. In both colonies chicks were fed with available in habitats near the colony, although in Tagus Estuary most prey originated from freshwater habitats. Diet of chicks remained constant through the development period and the proportions of crustaceans and fish consumed differed from other colonies elsewhere in Western Europe (Spain and the Netherlands). We conclude that in Portugal, spoonbills feed their chicks with prey commonly found in the vicinity of colonies. Prey originating from artificial habitats, particularly the invasive Louisiana crayfish Procambarus clarkii in the more recently occupied colony, were the most important items in the diet of chicks.