Age and sexual diVerences in the exploitation of two anthropogenic food resources for an opportunistic seabird

The availability of food resources has been suggested as a major factor in the substantial increase in reproductive output, survival, recruitment and, ultimately, population growth rates in most organisms. In fact, the artiWcial increase in food availability resulting from human activities has been suggested as a factor in the substantial increase in population size of several seabirds in recent decades. In the present study, our primary aim was to estimate the importance of the main natural prey and two alternative feeding resources, Wshery discards and the invasive American crayWsh Procambarus clarkii, for an opportunistic seabird, the Audouin’s gull Larus audouinii. We also assessed the inXuCommunicated by S. Garthe. J. Navarro · M. G. Forero Department of Conservation Biology, Estación Biológica de Doñana, CSIC, Av. Américo Vespucio, s/n, 41092 Sevilla, Spain D. Oro · M. Genovart Institut Mediterrani d’Estudis Avançats, IMEDEA (CSIC-UIB), C/Miquel Marqués 21, 07190 Esporles, Majorca, Spain