Forage fish to growing chicks: shared food resources between two closely related tern species

MARINAO, CRISTIAN; SUÁREZ, NICOLÁS; GATTO, ALEJANDRO; YORIO, PABLO

MARINE BIOLOGY

SPRINGER

Año: 2019 vol. 166

0025-3162

The assessment ofthe relevance of forage fish in seabird diet and how different speciespartition food resources is fundamental to understand predator preyrelationships. We assessed the importance of forage fish in the diet of Royal (Thalasseus maximus maximus) and Cayenne (T. sandvicensis eurygnathus) terns and theirpartitioning of food resources during the early and late chick stages of 2013and 2014 at a colony in Argentina. Direct observation of prey deliveries duringchick provisioning showed that diet composition of Royal and Cayenne ternscomprised at least 16 and 9 prey species, respectively. In both tern species,Argentine Anchovy (Engraulis anchoita) and five species of silversides (Odontesthes spp.) were the main prey fed to chicks (over 90% contribution,anchovy and silversides pooled). Both tern species fed their chicks withsimilar prey species, but Royal terns delivered, in general, larger prey thanCayenne terns. Both conventional and stable isotope methods showed a highoverlap in their trophic niches. Prey sizes delivered to chicks were larger inthe late chick stage and the second study season. Wind speed did not have asignificant effect on the frequency of the different prey species and sizesdelivered to chicks by both tern species. As anchovies and silversides arefishery targets, tern trophic requirements should be considered when planningfuture fisheries development and management.