RADIOTELEMETRIC MEASUREMENTS OF HEART-RATE IN SINGING BLACKBIRDS (TURDUS-MERULA)

The heart rate (HR) of 4 male Blackbirds was monitored by means of radiotelemetry in subsong and full song phases of singing birds. Results were obtained under 3 experimental conditions: (1) caged birds in the presence of conspecific male and female; (2) isolated caged birds in an anachoic chamber where playback experiments were conducted; (3) birds in an outdoor aviary. The singing of subsong could be related to 3 different types of HR curves: a) a marked acceleration combined with oscillations in longer cycles; b) a low and steady heart rate; c) a deceleration beginning abruptly with the onset of singing and ending abruptly when singing terminated. Strophes of full song were related to 4 kinds of HR curves: a) an acceleration; b) an abrupt deceleration; c) a steady HR on the level of the resting HR values; d) a biphasic course. The rather heterogeneous pattern of HR curves during singing suggests a hypothetic hierarchy related to motivation and function of certain song types. The low and stead curves express the lowest level, the decelerations a medium level and the accelerations the highest level of physiological strain or psychical tension. Strain and tension probably depend on the social context and the conditions in the birds' environment. The functions of the sounds may also differ and find expression in different modes of HR alterations.