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

QUINTANA, F.; YORIO, P.

JOURNAL OF FIELD ORNITHOLOGY

Año: 1999 vol. 70 p. 337 - 342

0273-8570

Severasl tudiesh ave shownt hat terms can be affectedb y kleptoparasitismfr omgulls. During 1992 and 1993 we studied kleptoparasitisma t a mixed-speciesc olony of KelpGulls (Larus dominicanus), Royal Terns (Sterna maxima), and Cayenne Terns (S. eurygnatha)at Punta Le6n, Chubut, Argentina. Robbing behavior did not involve aerial chases. KelpGulls remained at the terncry periphery and stole food from adults flying low over the colonywith food intended for chicks, from adult terms on the ground transferring food to theirchicks, or from chicks. The percentage of food robbed by Kelp Gulls from both tern specieswas8 .8% of food broughtt o the colony( n = 1131). Robbinge fficiencyw as5 8%. KelpG ullsrobbed significantlym ore food from Royalt han CayenneT erns (10.6 rs. 3.6%, respectively).The percentage of robbing attempts was also larger on Royal than Cayenne Terns (18.9 vs.5.7%). Robbinge fficiencyh, oweverw, ass imilarf or both tern species(5 6 and 63.2% for Royaland Cayenne Terns, respectively).K leptoparasitismo n Royal Terns within the colony wasrelated to the age of their chicks, being higher on terns with chicks older than 20 days ofage. The risk of a Royal Tern being robbed by Kelp Gulls was larger when it was feedingchicksa t the colonyt han on the beach (14.9% rs. 4.5%), althoughd ifferenceso bservedw erenot significant.