Cocoi Heron (Ardea cocoi) Connects Estuarine, Coastal, Limnetic and Terrestrial Environments: an Assessment Based on Conventional Dietary and Stable Isotope Analysis

Abstract

Wading birds are key components of wetlands, transporting matter, energy, contaminants and associated organisms among limnetic, estuarine, terrestrial and coastal ecosystems. The role of cocoi herons (Ardea cocoi) in connecting these ecosystems was studied in the only known estuarine and limnetic colonies in coastal plains of southern Brazil. Food obtained by parents around colonies when foraging for chicks and themselves was used to assess diet, by the analysis of 50 pellets, gastrointestinal contents and spontaneous regurgitated samples, as well as the analysis of stable isotopes (δ 13C and δ 15N) in the whole blood of 25 chicks. Cocoi herons were predominantly piscivorous in both environments, relying mainly on whitemouth croaker (Micropogonias furnieri) in the estuarine colony (47 % of samples and 36–56 % in the isotope mixing model), followed by Callinectes blue crabs and on trahira (Hoplias aff. malabaricus), in the limnetic colony (60 % of the dietary samples). However, for the limnetic colony, terrestrial and aquatic potential food sources contributed evenly to the isotopic mixing model. Furthermore, stable isotopes suggested that marine food sources, available on the coast 15 km away, were part of the diet of chicks in the limnetic colony. Complementary approaches used in the current study demonstrate that widely distributed, large-sized Ardea herons and other waterbirds are important for the connectivity of terrestrial and a range of aquatic environments. These birds contribute to the flow of matter and energy between wetlands and adjacent habitats and are key species for linking different food webs through complex and still poorly understood lateral subsides.