Adult South American Tern diet in relation to mate and chick prey requirements in Patagonia, Argentina

GATTO, A.; YORIO, P.

Victoria

Congreso; First World Seabird Conference; 2010

Breeding seabirds may show changes in the use of prey resources as a result of constraints imposed by courtship feeding or chick provisioning, often resulting in differences between self-feeding and prey provisioning. Deliveries during courtship feeding and the chick stage were quantified in South American Terns (Sterna hirundinacea) during the 2004 and 2005 breeding seasons at Punta Loma (42°S), Patagonia, Argentina, totaling 1840 prey items observed. Complementary stable isotope analysis was performed to assess isotopic niches and, using mixing models, evaluate the proportions of prey consumed by chicks and by adults during both the egg laying and chick rearing periods. South American terns at Punta Loma fed mainly on pelagic schooling fish, mostly Argentine anchovies Engraulis anchoita and silversides Odontesthes spp., but also included marine invertebrates and insects. Generalized linear models showed that adults delivered higher proportion of fish to their chicks than to their mates. Chicks were fed with a higher energy fish than mates (anchovies). Ordered Logistical Regression analysis showed that adults delivered larger fish to their mates than chicks. The diet of chicks was more diverse than that of mates, and showed higher amplitude in the use of fish sizes. Stable isotope analysis indicated that during the egg-laying and chick rearing periods, adults delivered higher energy and trophic level prey than that used for self-feeding.