Are stomach temperature recorders a useful tool for determining feeding activity?

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Despite a number of limitations, stomach temperature recorders are still commonly used to determine feeding activity in free-ranging marine predators. In this regard, it is important to improve the detection rate of these systems by, for instance, increasing the probability that a cold prey touches the sensors. In the present study, we compared the detection rates and mass estimations of water and fish prey ingested by captive king penguins using a two-point temperature recorder (STL) and a single, but large, point recorder (SICUP). Prey items were of different masses (5-45 g) and delivered at different frequencies (high vs. low). Ingestions were recorded as precipitous drop followed by an exponential rise (PDER). Overall, 57.9, 56.0 and 70.0% of the ingestions were detected by the SICUP and the upper and lower sensors of the STL, respectively. Our study confirmed that employing two sensors improves the detection of prey ingestion, but the detection of very small prey items remains insufficient and prey items swallowed at short intervals are detected as cumulative ingestion events. Nonetheless, the total mass of food ingested can be estimated with more than 70% confidence.