Age and sexual differences 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 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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The staff of the Ebro Delta NP and several volunteers, in special to Mario G. Dominguez, helped with logistics, including the ringing of gulls over the years. Laura Cardador provided valuable suggestions to improved previous versions of this manuscript. We would like to thank two anonymous reviewers for their valuable comments to improve this manuscript. Research funds were provided by the Spanish (REN2002-00450 and CGL2006-04325/BOS) and Andalucía Governments (P06-RNM-02362).

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Correspondence to Joan Navarro.

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Communicated by S. Garthe.

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Navarro, J., Oro, D., Bertolero, A. et al. Age and sexual differences in the exploitation of two anthropogenic food resources for an opportunistic seabird. Mar Biol 157, 2453–2459 (2010).

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  • Stable Isotope
  • Potential Prey
  • Demersal Fish
  • Natural Prey
  • Ebro Delta