Feeding behaviour of free-ranging penguins determined by oesophageal temperature

Sea birds play a major role in marine food webs, and it is important to det ermine when and how much they feed at sea. A major advance has been made by using the drop in stomach temperature after ingestion of ectothermic prey. This method is less sensitive when birds eat small prey or when the stomac h is full. Moreover, in diving birds, independently of food ingestion, ther e are fluctuations in the lower abdominal temperature during the dives. Usi ng oesophageal temperature, we present here a new method for detecting the timing of prey ingestion in free-ranging sea birds, and, to our knowledge, report the first data obtained on king penguins (Aptenodytes patagonicus). In birds ashore, which were hand-fed 2-15 g pieces of fish, all meal ingest ions were detected with a sensor in the upper oesophagus. Detection was poo rer with sensors at increasing distances from the beak. At sea, slow temper ature drops in the upper oesophagus and stomach characterized a diving effe ct per se. For the upper oesophagus only, abrupt temperature variations wer e superimposed, therefore indicating prey ingestions. We determined the dep ths at which these occurred. Combining the changes in oesophageal temperatu res of marine predators with their diving pattern opens new perspectives fo r understanding their foraging strategy, and, after validation with concurr ent applications of classical techniques of prey survey, for assessing the distribution of their prey.