Breeding diet of Cayenne and Royal terns in northern Patagonia, Argentina. Simposio: Population Status and Ecology of Royal and Sandwich Terns in the Americas

GATTO, A.; YORIO, P.

Veracruz, México

Simposio; IV North American Ornithological Conference; 2006

American Ornithologists' Union

Cayenne (Thalasseus sandvicensis eurygnatha) (CT) and Royal terns (Thalasseus maximus) (RT) breed sympatrically in Argentina. We present the first detailed information on their breeding diet. During 2004 and 2005 we made observations of prey delivered to mates and chicks at Punta León (43º04’ S, 64º29’ W). Observations were made during 116 hours (39 days) distributed throughout daylight hours and stages of the tidal cycle totalizing for both species 832 and 2940 prey delivered to mates and chicks, respectively. Diet of CT and RT comprised 9 and 10 prey species, respectively. Fish comprised 99% of the prey delivered by both terns in the two study years. Engraulis anchoita was the main prey for RT (65.8%; all other prey less than 20.7%), and Odonthestes sp for CT (38.9%; all other prey less than 29.2%). Prey diversity was significantly higher in 2004 than 2005 for both CT (1.39 vs 1.21) and RT (1.05 vs 0.96). CT delivered significantly smaller fish than RT. In both years, fish delivered to mates by CT and RT were significantly larger than those delivered to chicks. Implications for resource partitioning between terns and their interactions with coastal fisheries will be discussed.