Implantable data logging system for heart rate and body temperature: its application to the estimation of field metabolic rates in Antarctic predators.

The metabolic rate of free-ranging animals is difficult to measure, but of great importance in understanding the interactions of a species with its environment. Heart rate can, if correctly validated and calibrated, give an estimate of metabolic rate, with both a fine time resolution and over long periods. The telemetry of heart rate is well documented, but is not appropriate over long ranges (possibly several thousands of kilometres) or for diving species. An implantable data logger has therefore been developed for the long term recording of heart rate and body temperature. The logger is built using hybrid and ASIC construction techniques, weighs 20 g and measures 55 x 24 x 6 mm. The device is programmable, and its solid-state memory holds over 70 days of data if, for example, heart rate is counted and stored every minute. Current consumption is 155 microA while logging, 50 microA during a programmable initial delay period, and less than 1 microA when the logger closes down after filling its memory. These loggers have been deployed for two field seasons in gentoo penguins, black-browed albatross and fur seals.