title: Living on the edge: demography of the slender-billed gull in the Western Mediterranean.
abstract: Small and peripheral populations are typically vulnerable to local extinction processes but important for the metapopulation dynamics of species. The Slender-billed gull (Chroicocephalus genei) is a long-lived species breeding in unstable ephemeral coastal habitats. Their Western Mediterranean populations are relatively small and represent the edge of their global geographical distribution. At a local scale, using long-term data (14 years) on annual breeding success and capture-resights of marked individuals, we estimated and compared the vital rates and evaluated the connectivity of two Spanish populations (Ebro Delta and Doñana) varying in their local environmental conditions. At a metapopulation scale, we analyzed 22 years of data on breeding numbers to predict their future prospects by means of population demographic models. Local survival and breeding success of gulls from the Ebro Delta was lower than those from Doñana, which is likely the result of higher permanent emigration and/or winter mortality in the former. Gulls from the Ebro Delta wintered mostly in Mediterranean areas whereas those from Doñana did so in Atlantic coasts, where food availability is higher. Whereas adult local survival was constant, juvenile local survival showed temporal parallel variations between colonies, probably related to natal dispersal to other breeding colonies. Our results suggested that dispersal was higher at the Ebro Delta and gulls emigrating from their natal colonies settled preferentially in close patches. We found large fluctuations in breeding numbers among local populations probably related to the fact that the Slender-billed gull is a species adapted to unstable and unpredictable habitats with high abilities to disperse between suitable patches depending on environmental stochastic conditions during breeding.
authors.affiliation: Department of Conservation Biology, Estación Biológica de Doñana (CSIC), Sevilla, Spain; Population Ecology Group, Institut Mediterrani d'Estudis Avançats, IMEDEA (CSIC-UIB), Esporles, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Sanz-Aguilar
authors.affiliation: Population Ecology Group, Institut Mediterrani d'Estudis Avançats, IMEDEA (CSIC-UIB), Esporles, Spain.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Tavecchia
authors.affiliation: Laboratorio de SIG y Teledetección (LAST-EBD), Estación Biológica de Doñana (CSIC), Sevilla, Spain.
authors.forename: Isabel
authors.initials: I
authors.lastname: Afán
authors.affiliation: Department of Conservation Biology, Estación Biológica de Doñana (CSIC), Sevilla, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Ramírez
authors.affiliation: Population Ecology Group, Institut Mediterrani d'Estudis Avançats, IMEDEA (CSIC-UIB), Esporles, Spain; Institut des Sciences de l'Evolution, UMR 5554, CNRS, Université de Montpellier 2, Montpellier, France.
authors.forename: Aggeliki
authors.initials: A
authors.lastname: Doxa
authors.affiliation: Unitat d'Ecosistemes Aquatics, Institut de Reserca i Tecnologie Agroalimentaries, Sant Carles de la Ràpita, Spain.
authors.forename: Albert
authors.initials: A
authors.lastname: Bertolero
authors.affiliation: Department of Conservation Biology, Estación Biológica de Doñana (CSIC), Sevilla, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Gutiérrez-Expósito
authors.affiliation: Department of Conservation Biology, Estación Biológica de Doñana (CSIC), Sevilla, Spain.
authors.forename: Manuela G
authors.initials: MG
authors.lastname: Forero
authors.affiliation: Population Ecology Group, Institut Mediterrani d'Estudis Avançats, IMEDEA (CSIC-UIB), Esporles, Spain.
authors.forename: Daniel
authors.initials: D
authors.lastname: Oro
mesh_terms: D000818:Animals; D001947:Breeding; D046091:Charadriiformes; D019083:Mediterranean Region; D011157:Population Dynamics; D012621:Seasons