ORIGINAL ARTICLE Foraging movements of Magellanic Penguins Spheniscus magellanicus in the Beagle Channel, Argentina, related to tide and tidal currents Andrea Raya Rey • Charles-Andre ´ Bost • Adria ´n Schiavini • Klemens Pu ¨tz Received: 22 October 2009 / Revised: 22 March 2010 / Accepted: 28 April 2010 Ó Dt. Ornithologen-Gesellschaft e.V. 2010 Abstract This study investigates the movements of Magellanic Penguins Spheniscus magellanicus breeding on Isla Martillo during the early chick-rearing period. Foraging paths were reconstructed using GPS loggers that registered the penguins 0 geographic position, water tem- perature and depth at regular intervals. The relationship between penguins 0 movements and search strategies, tide and tidal currents were assessed. Mean trip duration was on average 14.7 ± 6.9 h (33% overnight), and the maximum distance reached was 24 ± 10 km. All penguins studied foraged to the east of the colony. We identified three phases based on the sinuosity and speed of the trajectory: transit, central and return. Foraging effort was higher during the central phase, followed by the transit phase, and lower in the return phase. Foraging success, measured as the percentage of time at the bottom during each phase, was also highest during the central phase. In all birds studied, the central phase of the foraging trip took place during ebb tide, and birds travelled to the foraging areas with flow tide running in the same direction of displace- ment. Our study suggests that penguins take advantage of tidal currents to facilitate their movements to and from the main foraging area, thereby reducing the energy expended. Moreover, we suggest that piscivorous diving birds may enhance their catch rate during ebb tide when fish are more concentrated near the channel bed. Keywords Spheniscus magellanicus Á Foraging movements Á Search strategy Á Tide and tidal currents Introduction Seabirds are mobile species that depend on a spatially and temporally heterogeneous environment (Hunt 1999). As a consequence seabirds exhibit considerable variation in their foraging behaviour or at-sea distribution. Prey avail- ability is related to the physical and biological properties of the ocean, such as depth (Hastie et al. 2003), hydrological structure (Charrassin and Bost 2001), and substrate type (Tollit et al. 1998) and, in near-shore waters, tidal effects (Chen et al. 1999; Holm and Burger 2002; Zamon 2003). Therefore, habitat utilisation by predators is assumed to reflect the quality and availability of resources in an area (Davoren et al. 2003; Laidre et al. 2004). Predators must make optimal decisions about where and how to forage to maximise both their efficiency and, ultimately, their fitness (Stephens and Krebs 1986). Seabirds are thought to follow complex scale-driven strategies when searching for food (Weimerskirch et al. 2007; Fritz et al. 2003). Establishing the factors driving the movements of free-ranging seabirds is then crucial for a better understanding of their Communicated by P. H. Becker. A. Raya Rey (&) Á A. Schiavini Consejo Nacional de Investigaciones Cientı ´ficas y Te ´cnicas, CADIC, Bernardo Houssay 200, (V9410BFD), Ushuaia, Tierra del Fuego, Argentina e-mail: arayarey@cadic.gov.ar C.-A. Bost Centre d’E ´ tudes Biologiques de Chize ´, Centre National de la Recherche Scientifique, 79360 Villiers en Bois, France A. Schiavini Wildlife Conservation Society, 2300 Southern Blvd, Bronx, NY 10460, USA K. Pu ¨tz Antarctic Research Trust, PO Box 685, Stanley FIQQ 1ZZ, Falkland Islands 123 J Ornithol DOI 10.1007/s10336-010-0531-y