Age and sexual differences in the exploitation of two anthropogenic food resources for an opportunistic seabird |
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Authors: | Joan Navarro Daniel Oro Albert Bertolero Meritxell Genovart Antonio Delgado Manuela G Forero |
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Institution: | 1. Department of Conservation Biology, Estación Biológica de Do?ana, CSIC, Av. Américo Vespucio, s/n, 41092, Sevilla, Spain 5. Institute of Marine Science (ICM-CSIC), Passeig Marítim de la Barceloneta 27-49, 08003, Barcelona, Spain 2. Institut Mediterrani d’Estudis Avan?ats, IMEDEA (CSIC-UIB), C/Miquel Marqués 21, 07190, Esporles, Majorca, Spain 3. IRTA Ecosistemes Aquàtics, Sant Carles de la Ràpita, Carretera de Poble Nou km 5, 43540, Sant Carles de la Ràpita, Spain 4. Laboratorio de Biogeoquímica de Isótopos Estables, Instituio Andaluz de Ciencias de la Tierra, CSIC, Camino del Jueves s/n, 18100, Armilla, Granada, Spain
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Abstract: | 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 artificial 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, fishery discards and the invasive American crayfish Procambarus clarkii, for an opportunistic seabird, the Audouin’s gull Larus audouinii. We also assessed the influence of age and sex in the use of those three types of food. For this purpose, we compared the
analyses of δ15N and δ13C in blood of male and female adults of known age and chicks with those in their potential prey. Our results reveal sex-related
and age-related differences in the consumption of fish discards, small pelagic fish and American crayfish. Differences in
the diet of males and females and also between adults and chicks could be related to different nutritional requirements. Age
differences were probably related to their different foraging proficiency and the tendency of young breeders to opportunistically
exploit anthropogenically derived food. This study illustrates the importance of considering the age and sex of individuals
to obtain feasible dietary information and to understand how the exploitation of food of human origin could affect population
growth. |
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