ORIGINAL PAPER Yan Ropert-Coudert á Akiko Kato á Julien Baudat Charles-Andre Bost á Yvon Le Maho á Yasuhiko Naito Feeding strategies of free-ranging Ade  lie penguins Pygoscelis adeliae analysed by multiple data recording Accepted: 15 January 2001 / Published online: 3 March 2001 Ó Springer-Verlag 2001 Abstract The ®ne-scale feeding behaviour of free-rang- ing AdeÂlie penguins Pygoscelis adeliae) during a single foraging trip was investigated by monitoring three parameters simultaneously at a frequency of 1 Hz, these being depth, swim speed and oesophagus temperature. Ingestion events were detected as abrupt drops in the oesophageal temperature and related to the birds' foraging behaviour. Although a high percentage of oesophageal temperature loggers were rejected, 1 com- plete foraging trip was recorded for all the 3 parameters from 1 bird while 92% and 67% of the foraging trip was recorded for 2 other birds; 12.3% of the temperature drops occurred at the surface but they were mainly small, except 61 of them probably representing snow ingestion while the birds were on land. All other drops were observed during dives, 88% of them during the undulatory and occasionally the ascent) phase of dives deeper than 40 m. The mean swim speed during non- feeding shallow and exploratory dives was relatively constant throughout the dive, around 2.1 m s ±1 , whereas during feeding deep dives, swim speed during the und- ulatory phase was lower 1.71 m s ±1 ) than during the descent and ascent and was characterised by a series of rapid accelerations and decelerations; 42.6% of these accelerations were followed by one or more ingestion events and birds swam upward in 60% of the accelera- tions. Such multiple data recording opens new paths for the examination of the decision-making processes in foraging penguins. Introduction Any assessment of the role of animals within ecosystems should consider feeding habits of primary importance Collinvaux 1986). Studies on the feeding ecology of air- breathing marine animals are often logistically dicult since direct observation is impossible. Consequently, numerous data loggers have recently been developed to examine various parameters as a function of time Le Maho 1994). Some of the most promising work using data loggers to assess the role of marine endotherms has investigated the internal temperature of endothermic marine top predators Wilson and Culik 1991; Wilson et al. 1992; Kato et al. 1996) so as to determine when prey are ingested in tandem with parameters of the animals' foraging behaviour e.g. Wilson et al. 1993; Weimerskirch et al. 1994). Recently, a logger with par- ticularly ®ne resolution was introduced for determining feeding activity by monitoring oesophageal temperature Ancel et al. 1997). This means that, with appropriate complementary data on animal activity, it should be possible to determine those features of foraging beha- viour that lead to the successful capture and ingestion of prey. We present the ®rst data derived from the use of this oesophageal temperature recording system on free-living AdeÂlie penguins Pygoscelis adeliae), simultaneously equipped with depth and swim-speed loggers and re- cording data with ®ne temporal resolution. These birds feed mainly on krill Euphausia superba and E. crystall- orophias Williams 1995), although ®sh may sometimes be taken e.g. Ridoux and Oredo 1989). A dietary study conducted on AdeÂlie penguins in AdeÂlie Land showed that euphausids dominate during the ®rst part of the breeding season Ridoux and Oredo 1989). Al- though no dietary data were collected during our study, Polar Biol 2001) 24: 460±466 DOI 10.1007/s003000100234 Y. Ropert-Coudert &) Department of Polar Sciences, Graduate University for Advanced Studies, National Institute of Polar Research, 1-9-10 Kaga, Itabashi-ku, Tokyo 173-8515, Japan E-mail: yan@nipr.ac.jp Fax: +81-3-39625743 A. Kato á Y. Naito National Institute of Polar Research, 1-9-10 Kaga, Itabashi-ku, Tokyo 173-8515, Japan J. Baudat á C.-A. Bost á Y. Le Maho Centre d'Ecologie et de Physiologie EnergeÂtiques, Centre National de la Recherche Scienti®que, 23 rue Becquerel, 67087 Strasbourg, France