ORIGINAL PAPER How age and sex drive the foraging behaviour in the king penguin Maryline Le Vaillant • Ce ´line Le Bohec • One ´sime Prud’Homme • Barbara Wienecke • Yvon Le Maho • Akiko Kato • Yan Ropert-Coudert Received: 13 June 2012 / Accepted: 3 January 2013 / Published online: 20 January 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract As predicted by life history theory, once recruited into the breeding population and with increasing age, long-lived animals should be able to manage more efficiently the conflict between self-maintenance and reproduction. Consequently, breeding performances should improve with age before stabilizing at a certain level. Using temperature–depth recorders and isotopic analysis, we tested how age affects the foraging behaviour of king penguin Aptenodytes patagonicus during one trip in the chick-rearing phase. Depending on sex and age, king penguins expressed two different foraging strategies. Older birds gained more daily mass per unit body mass than younger ones. Older females conducted shorter trips, dived deeper and performed more prey pursuits. They also had higher blood levels of d 15 N than younger individuals and males indicating sex- and age-specific dietary regimes. However, we found no differences in carbon isotopic sig- nature, suggesting that individuals exploited the same foraging areas independently of sex and age. Our results suggest that king penguins are able to increase the quantity of energy extracted with increasing age and that such a strategy is sex-related. Our study is the first to reveal of an interaction between age and sex in determining foraging efficiency in king penguins. Introduction Intrinsic factors, such as age or sex (Daunt et al. 2007; Weimerskirch et al. 1997; Welcker et al. 2009; Pinet et al. 2012), are known to affect an individual’s ability to forage, and the subsequent energy allocation to different functions (e.g. reproduction and self-maintenance). For example, sex influences foraging behaviour in species where sex-specific strategies result from sexual dimorphism that causes dif- ferences in hunting abilities (Kato et al. 2000), but also in monomorphic species where density-dependent responses may shape foraging strategies to decrease intra-specific competition (Lewis et al. 2005). With age, the individual improves its knowledge of the environment (Pa ¨rt 2001), can expand the range of dietary items available (Ru ¨tz et al. Communicated by S. Garthe. Electronic supplementary material The online version of this article (doi:10.1007/s00227-013-2167-y) contains supplementary material, which is available to authorized users. M. Le Vaillant (&)  C. Le Bohec  O. Prud’Homme  Y. Le Maho  A. Kato  Y. Ropert-Coudert Institut Pluridisciplinaire Hubert Curien, Universite ´ de Strasbourg, 23 rue Becquerel, 67087 Strasbourg, France e-mail: levaillant.mary@gmail.com M. Le Vaillant  C. Le Bohec  O. Prud’Homme  Y. Le Maho  A. Kato  Y. Ropert-Coudert CNRS, UMR7178, 23 rue Becquerel, 67037 Strasbourg, France C. Le Bohec Centre Scientifique de Monaco, 8 quai Antoine 1er, 98000 Monaco, Principality of Monaco C. Le Bohec LEA 647 ‘BioSensib’ CSM-CNRS, 8 quai Antoine 1er, 98000 Monaco, Principality of Monaco C. Le Bohec Nordic Centre for Research on Marine Ecosystems and Resources under Climate Change (NorMER), Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, P.O. Box 1066, Blindern, 0316 Oslo, Norway B. Wienecke Australian Antarctic Division, Channel Highway, Kingston, TAS 7050, Australia 123 Mar Biol (2013) 160:1147–1156 DOI 10.1007/s00227-013-2167-y