Keywords
acoustic degradation
Zonotrichia capensis
playback
song
Abstract
The song of the Rufous-collared Sparrow (Zonotrichia capensis) has two parts: an introduction and a final portion referred to as "theme" and "trill", respectively. The Alerted Detection Hypothesis suggests that song structure is adaptive for long-range communication in a noisy environment. Besides, it proposes that the theme evolved as an alerting component which warns receivers about the imminence of the informative part of the signal: the trill. We tested this hypothesis with a playback design using complete songs, themes and trills, in both normal and acoustically degraded condition. The Rufous-collared Sparrows responded more to complete and normal stimuli than to the theme, trill, and degraded stimuli, respectively. In addition, there were no differences in the strength of response elicited by themes and trills. These results contrast with the predictions of the Alerted Detection Hypothesis, according to which, only complete normal or degraded songs as well as normal trills, would have evoked responses.
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