FACTORS AFFECTING KLEPTOPARASITISM AND PREDATION RATES UPON A COLONY OF AUDOUINS GULL (LARUS-AUDOUINII) BY YELLOW-LEGGED GULLS (LARUS-CACHINNANS) IN SPAIN
D. Oro et A. Martinezvilalta, FACTORS AFFECTING KLEPTOPARASITISM AND PREDATION RATES UPON A COLONY OF AUDOUINS GULL (LARUS-AUDOUINII) BY YELLOW-LEGGED GULLS (LARUS-CACHINNANS) IN SPAIN, Colonial waterbirds, 17(1), 1994, pp. 35-41
We studied part of the world's largest breeding colony of Audouin's Gu
ll (Larus audouinii) in the Ebro Delta, NE Spain, in 1992, to evaluate
predation and kleptoparasitism effects by Yellow-legged Gulls (Larus
cachinnans). Kleptoparasitic attacks were the most frequent kind of di
sturbance, concentrated during the period when Yellow-legged Gull chic
ks were being raised. This also coincided with a moratorium period for
commercial fisheries when the food resource provided by fishing vesse
ls was unavailable. More attacks occurred either early or late in the
day when the Audouin's Gulls returned to the colony from feeding sites
. The success rate was higher for long chases and for large parasitic
groups of gulls. Subadult and adult Yellow-legged Gulls had similar kl
eptoparasitic success. Yellow-legged Gull predation on Audouin's Gull
eggs and chicks was low and appeared not to affect the breeding perfor
mance of Audouin's Gull.