We examined the accuracy of both stomach and oesophagus temperature sensors-deployed on captive Brandt's cormorants-for determination of the mass of food ingested and the number of prey items swallowed. The oesophageal temperature sensor was a better detector of all feeding events, including that of small prey which were missed by the stomach sensor. Adapted to free-ranging animals (and coupled to data loggers for recording seawater temperature), oesophagus temperature recorders, in conjunction with both recordings of energy expenditure (e.g. doubly labelled water, heart rate) and determination of position (e.g. Argos transmitter, time/depth recorder), should provide further important insights into the foraging success of marine endotherms.