Measurement of digestive variables in free-living animals: gastric motility in penguins during foraging

A stomach motility probe was developed in order to investigate digestive regulation in penguins. The sensor was a piezoelectric PVDF film which generated a voltage according to the extent and the speed at which the film was bent. This gave an estimate of the intensity of the contraction waves. Since measurements over periods of several days under natural conditions were necessary for the study, a data logger was used for data acquisition. The whole unit, incorporated in a titanium tube, was fed to the penguins and allowed measurement in free-living animals. Since it was not considered necessary to detect every single contraction wave but rather to get an overall picture regarding the phases of high or low stomach churning, the sensor was coupled to a voltage integrator with a free-adjustable time constant. This setup allowed the signals of one or several contraction waves to be summed. The data were stored in a two-channel data logger with 8 bit resolution and a memory of 128 kB. The logging interval was programmable. The second channel was used for recording the temperature to provide information about the feeding behaviour of the animals. key words: digestive regulation, telemetry, data logger, stomach temperature, thermoregulation