Radiotelemetric monitoring of heart-rate responses to song playback in blackbirds (Turdus merula)

Summary

The heart rate (HR) of three male and five female European blackbirds (Turdus merula) was monitored by radiotelemetry under three conditions: in a dark cage, in a lighted cage, and in an outdoor aviary. In all three, the response to recorded bird song was tested.

The resting HR in the cage ranged from 4.8 to 6.3 beats per second. The HR of all the birds changed in response to playback of conspecific song as well as of the songs of other species. In 68% of trials a typical biphasic HR curve was obtained, with acceleration followed by deceleration (Fig. 2). The time from stimulus onset to the second curve inflection (t _iII) averaged 15–18 s; this was significantly longer for conspecific than for heterospecific song. The parameter t _iII was used as a basic measure of the response.

The reaction of the males was longer-lasting than that of the females. The possibility that this reflects the territorial role of the songs is discussed. Response durations were longest in the dark cage, and shortest in the aviary. The reason is thought to be the gradation in total stimulus input available to the bird.

The results suggest that the HR response consists of an unspecific component (acceleration) plus a component specific to bird sounds (deceleration). At this fundamental level of stimulus processing it is possible to study reactions to single strophes not only in males, as with more traditional methods, but also in females and young birds.