Patterns of resource utilization during chick rearing season by gulls and terns breeding in a Mediterranean lagoon

catalaLes nostres analisis van suggerir diferencies d’explotacio dels recursos i van assignar les especies en tres grups: (1) alimentant-se als camps d'arros i la llacuna (gavina capnegra Larus melanocephalus, gavina corsa L. audouinii, gavia argentat mediterrani L. michahellis, curroc Gelochelidon nilotica i fumarell de galta blanca Chlidonias hybrida); (2) especies que combinen els camps d'arros i els estanys salobrencs (gavina vulgar Chroicocephalus ridibundus, gavina capblanca C. genei); i (3) especies alimentant-se a aigues obertes, particularment a la mar (xatrac becllarg S. sandvicensis, xatrac comu S. hirundo, mongeta Sternula albifrons). Els nostres resultats van mostrar que les especies amb les poblacions reproductores locals mes grans (i.e., xatrac comu, gavina vulgar, xatrac becllarg, gavina corsa, i curroc) explotaven amb exit els recursos mes avantatjosos (i.e., arrossars i aigues marines) en termes d'abundancia de preses i de sincronitzacio amb el creixement de les cries. L'extensa transformacio dels habitats palustres naturals al lloc d'estudi i la manca d’habitats d’alimentacio alternatius i productius durant l'estacio reproductora, poden posar en perill les colonies de gavines i xatracts que es van establir tot seguint esforCos recents de conservacio. EnglishPatterns of resource utilization, habitat use for feeding and foraging techniques within a gull and tern breeding community were evaluated in a coastal lagoon of the western Mediterranean (l’Albufera de Valencia, E Spain) during the chick rearing season. Five habitat types were identified as foraging habitats at the study site; all were exploited to a variable extent indicating different access to food resources and foraging divergence among the species. Our analyses suggested differences in resource exploitation and structured the species into three groups of (1) species foraging the rice paddies and the lagoon (Mediterranean gull Larus melanocephalus, Audouin's gull L. audouinii, yellow-legged gull L. michahellis, gull-billed tern Gelochelidon nilotica and whiskered tern Chlidonias hybrida); (2) species combining the rice paddies and the brackish marshes (black-headed gull Chroicocephalus ridibundus, slender-billed gull C. genei); and (3) species foraging the open waters, particularly at sea (sandwich tern S. sandvicensis, common tern S. hirundo, little tern Sternula albifrons). Our results showed that the species with larger local breeding population (i.e., common tern, black-headed gull, sandwich tern, Audouin's gull, and gull-billed tern) were successfully exploiting the most advantageous resources (i.e., rice field marshes and marine waters) in terms of prey abundance and timing with brood rearing. The extensive transformation of natural wetland habitats at the study site and the lack of alternative, productive foraging habitats during the breeding season may endanger the thriving gull and tern colonies that came along with recent conservation efforts.