Kleptoparasitism by Kelp Gulls on Royal and Cayenne Terns at Punta-Leon, Argentina

QUINTANA, F.; YORIO, P.

JOURNAL OF FIELD ORNITHOLOGY

Año: 1999 vol. 70 p. 337 - 342

Several studies have shown that terns can be affected by kleptoparasitism from gulls. During 1992 and 1993 we studied kleptoparasitism interactions at a mixed-species colony of Kelp Gulls, Larus dominicanus, Royal Terns, Sterna maxima, and Cayenne Terns, S. eurygnatha, at Punta León, Chubut, Argentina. Robbing behavior did not involve aerial chases. Kelp Gulls remained at the ternery periphery and stole food from adults flying low over the colony with food intended for chicks, from adult terns on the ground transferring food to their chicks, or from chicks. The percentage of  food robbed by Kelp Gulls from both tern species was 8.8% of food brought to the colony (n = 1131). Robbing efficiency was 58%. Kelp Gulls robbed significantly more food from Royal than Cayenne Terns (10.6 vs 3.6%, respectively). The percentage of robbing attempts was also larger on Royal than Cayenne Terns (18.9 vs 5.7%). Robbing efficiency, however, was similar for both tern species (56 and 63.2% for Royal and Cayenne Terns, respectively). Kleptoparasitism on Royal Terns within the colony was related to the age of their chicks, being higher on terns with chicks older than 20 days of age. The risk of a Royal Tern being robbed by Kelp Gulls was larger when it was feeding chicks at the colony than on the beach (14.9% vs 4.5%), although differences observed were not significant.