Scientia Marina, Vol 67, No S2 (2003)

Kleptoparasitism, disturbance and predation of yellow-legged gulls on Audouin's gulls in three colonies of the western Mediterranean


https://doi.org/10.3989/scimar.2003.67s289

Alejandro Martínez-Abraín
Institut Mediterràni d’Estudis Avançats IMEDEA (CSIC-UIB) - CPEMN Conselleria de Medi Ambient, Generalitat Valenciana, Spain

Jacob González-Solis
Dept. Biología Animal, Vetebrats, Universitat de Barcelona, Spain

Vittorio Pedrocchi
Dept. Biología Animal, Vetebrats, Universitat de Barcelona, Spain

Meritxell Genovart
Institut Mediterràni d’Estudis Avançats IMEDEA (CSIC-UIB) - Dept. Biología Animal, Vetebrats, Universitat de Barcelona, Spain

Joan Carles Abella
Dept. Biología Animal, Vetebrats, Universitat de Barcelona, Spain

Xavier Ruiz
Dept. Biología Animal, Vetebrats, Universitat de Barcelona, Spain

Juan Jiménez
CPEMN Conselleria de Medi Ambient, Generalitat Valenciana, Spain

Daniel Oro
Institut Mediterràni d’Estudis Avançats IMEDEA (CSIC-UIB) - Dept. Biología Animal, Vetebrats, Universitat de Barcelona, Spain

Abstract


The impact of yellow-legged gulls on Audouin´s gulls was studied by means of observations from a blind, at the Ebro Delta, the Chafarinas Islands and the Columbretes Islands colonies, during different stages of Audouin´s Gulls breeding cycle. The rates of predation (upon eggs and chicks) and kleptoparasitism (aerial and on courtship and chick-feeding regurgitates) were recorded to evaluate this impact. Kleptoparasitism and predation rates recorded at the three colonies may be considered low when compared with similar studies dealing with other gull species. It seems that interactions did not represent a threat to the population dynamics of Audouin´s Gulls in any of the three colonies. The highest rates of aerial kleptoparasitism, courtship feeding and chick mortality were recorded at the Columbretes Islands, and the lowest at the Ebro Delta. The ratio of the number of yellow-legged gulls to the number of Audouin´s gulls seems to influence the rate of disturbances. Food availability was also likely to play an important role in the number of interactions, which increased when food was in shorter supply. The study at the Ebro Delta and Chafarinas Islands was restricted to some subcolonies and hence results may not be necessarily representative of the entire colonies. The existence of some yellow-legged gull individuals specialised as predators was recorded. Finally, we discuss the suitability of several conservation measures commonly applied in colonies where both species breed syntopically.

Keywords


kleptoparasitism; predation; disturbance; gulls; Columbretes; Chafarinas; Ebro Delta; conservation; seabirds

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