Abstract
One of the main threats to Audouin´s gull ( Larus audouinii ) at Chafarinas Islands is predation on eggs and chicks by the yellow-legged gull ( Larus cachinnans ). During the 1999 and 2000 breeding seasons we tested the effects of supplementary refuge availability on chick survival. Well before the laying period, nine adjacent enclosures were erected inside Audouin´s gull´s breeding grounds and some of them were supplied with artificial refuges. Our results showed significantly greater chick survival in the enclosures with artificial refuges than in control ones. In 2000, an overall lower breeding success of Audouin´s gull and a dilution of the refuge effect were observed. These results were probably related to food-shortage that year. We suggest that, along with other factors, an increase in refuge availability may significantly enhance Audouin´s gull chick survival.
Highlights
The Chafarinas Islands archipelago holds important colonies of Audouin’s (Larus audouinii) and yellow-legged gulls (Larus cachinnans), with 3,320 and 3,370 breeding pairs respectively (Ruiz et al., 2000).Earlier studies in different colonies have reported a high degree of interaction between the two species (de Juana et al, 1984; Bradley, 1988; Oro and Martínez-Vilalta, 1994)
During the 1999 and 2000 breeding seasons we tested the effects of supplementary refuge availability on chick survival
Well before the laying period, nine adjacent enclosures were erected inside Audouin’s gull’s breeding grounds and some of them were supplied with artificial refuges
Summary
The Chafarinas Islands archipelago holds important colonies of Audouin’s (Larus audouinii) and yellow-legged gulls (Larus cachinnans), with 3,320 and 3,370 breeding pairs respectively (Ruiz et al., 2000).Earlier studies in different colonies have reported a high degree of interaction between the two species (de Juana et al, 1984; Bradley, 1988; Oro and Martínez-Vilalta, 1994). Factors like food availability, the relative numbers of both species or the colony size can influence the intensity of these interactions (Witt et al, 1981; de Juana et al, 1984; Varela and de Juana, 1986; Bradley, 1988; Oro and Martínez-Vilalta, 1994; Oro et al, 1996a; Oro et al, 1996b; Ruiz et al, 1996; González-Solís et al, 1997b). The effects of yellow-legged gull predation on Audouin’s gull productivity depend largely on the relative numbers of the two species (Oro et al, 1996a; González-Solís et al, 1997b). This is because yellowlegged gull individuals predating on Audouin’s gulls are specialists in the use of this resource and their numbers are proportional to colony size. When Audouin’s and yellow-legged gulls breed in imbalaced proportions the effects can range from devastating to negligible, depending on which species dominate (Oro et al, 1996b)
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