Diet and resource partitioning between egrets and herons in an estuarine colony in southern Brazil

Abstract Herons are predators at high levels of the trophic webs in aquatic and adjacent terrestrial environments. They often breed sympatrically, forming colonies with multiple species that play key roles in the transport of nutrients and can serve as environmental sentinels. However, studies evaluating foraging habits, resource partitioning, and niche overlap are still scarce. We used complementary stable isotopes of carbon and nitrogen, and food remains analyses to investigate diet overlap among cattle egret ( Bubulcus ibis ), snowy egret ( Egretta thula ), and black-crowned night heron ( Nycticorax nycticorax ) at the Lagoa dos Patos estuary, southern Brazil. These species fed on vertebrates (mainly fish but also anurans and bird chicks) and arthropods (insects, arachnids, and crustaceans) in varying proportions. Similarly, stable isotopes demonstrated assimilated sources from estuarine, limnetic, and terrestrial areas, with food items differing in proportions. The diet of cattle egrets was composed mainly of terrestrial prey, while snowy egrets fed mainly on aquatic prey. Black-crowned night herons had a generalist diet and the highest isotopic niche breadth, which overlapped with other species. Our study demonstrated that small-to-medium-sized herons have trophic plasticity and despite sharing food items in different proportions, they show a distinction in at least one of the niche dimensions (temporal, spatial, or trophic), which allows for the coexistence of sympatric species in multispecies colonies.