Interspecific kleptoparasitism in Audouin’s Gull Lams audouinii at the Ebro Delta, northeast Spain: a behavioural response to low food availability

Kleptoparasitism of Audouin’s Gull Lams audouinii on other seabirds, a foraging behaviour previously unrecorded for the species, was studied in the Ebro Delta, northeast Spain, during 1992. The relationship between kleptoparasitism and trawler activity was assessed through changes in the availability of fish discards brought about by a trawling moratorium. When trawlers are not active, Audouin’s Gulls use different feeding strategies, such as interspecific kleptoparasitism. Audoin’s Gulls appeared to prefer to Meptoparasitize terns rather than gulls, but the success rate on gulls was higher. Most of the attacks were performed by single Audouin’s Gulls, although success per attack improved with group size. During the trawling moratorium, the existence of large seabird colonies in the Ebro Delta acted as a buffer for Audouin’s Gull through kleptoparasitism, compensating partly for the reduced food supply. Until the establishment of a breeding colony in the Ebro Delta in 1981. Audouin’s Gull Lams audouinii was considered threatened because of its small population size. Now, the total world population of Audouin’s Gull has increased dra