Tracking macaroni penguins during long foraging trips using 'behavioural geolocation

The movement of marine vertebrates has been tracked using a variety of techniques, all of which depend on the external attachment of a transmitting or recording device. However, these devices can have negative effects on the subject animals, limiting both the quantity and quality of data collected. We present a new method for monitoring large-scale movement of marine vertebrates that uses behavioural data stored on a surgically implanted data logger. The technique (‘behavioural geolocation’) relies on the principles of light-based geolocation but rather than measuring ambient light levels, changes in diving behaviour associated with sunrise and sunset are used to infer daylength and time of local sunrise, and hence location. We present data from a trial, post-hoc, analysis of diving data collected from macaroni penguins Eudyptes chrysolophus during long foraging trips associated with incubation and preparation for moult. Our results showed that the penguins usually travelled to the polar frontal zone to the north of their breeding colony at South Georgia, an area broadly consistent with previously measured behaviour and the availability of preferred prey at this period of the annual cycle.