A radiotelemetry system for analyzing heart rate responses during playback experiments in blackbirds (Turdus merula )

In acoustical stimulus-response tests on European blackbirds (Turdus merula ) in cages and an outdoor aviary, alteration in heart rate (HR) was used to measure reaction strenght. HR was measured by radiotelemetry. The miniature transmitters newly developed for this task had to fulfill the following requirements: Simultaneous recordings of HR in several interacting animals; uninterrupted transmission of HR signals, sufficient range and battery life combined with low weight and easy handling properties. The miniature transmitters successfully used in this experiment had a quartz-stabilized oscillator. They weighed between 4.1 and 5.2 g and had a range of 3 m and a lifetime of 72 hrs (circuit diagram, Fig.1). The transmitted signal corresponded to a unitary impulse representing the S-wave of the ECG (Fig. 4b). Implanted electrodes were used to record ECG potentials. The transmitter was carried by the birds like a small rucksack tied to their backs. Electrode implantation and transmitter installation are described in detail. HR signals stored on audio tape were later transformed to frequency curves on a chart recorder (Fig. 3, 4a). Typical HR response curves are shown (Fig. 5). Statistical analysis of the data was performed on a DEC-PDP-11 computer using a special set of programs. The system has been successfully used to provide answers to experimental questions not previously obtainable with classical methods.