摘要
Multi-component signals contain multiple signal parts expressed in the same physical modality. One way to identify individual components is if they are produced by different physical mechanisms. Here, I studied the mechanisms generating acoustic signals in the courtship displays of the Calliope hummingbird Stellula calliope. Display dives consisted of three synchronized sound elements, a high-frequency tone （hfl）, a low frequency tone （lft）, and atonal sound pulses （asp）, which were then followed by a frequency-modulated fall. Manipulating any of the rectrices （tail-feathers） of wild males impaired production of the lft and asp but not the hfl or fall, which are apparently vocal. I tested the sound production capabilities of the rectrices in a wind tunnel. Single rectrices could generate the lft but not the asp, whereas multiple rectrices tested together produced sounds sitlfilar to the asp when they fluttered and collided with their neighbors percussively, representing a previously unknown mechanism of sound production. During the shuttle display, a trill is generated by the wings during pulses in which the wingbeat frequency is elevated to 95 Hz, 40% higher than the typical hovering wingbeat frequency. The Calliope hummingbird courtship displays include sounds produced by three independent mechanisms, and thus include a minimum of three acoustic signal components. These acoustic mechanisms have different constraints and thus potentially contain different messages. Producing multiple acoustic signals via multiple mechanisms may be a way to escape the constraints present in any single mechanism .
基金
Acknowledgments I thank S. Weinstein, A. Varma, and T. Feo for assistance in the field
L. Benedict and T. Libby for use of equipment, J. Brown for accommodations, and G. Weston-Murphy for assistance with the wind tunnel. Walter Nussbaumer kindly allowed use of a photo. The manuscript was improved by comments from T. Feo and two anonymous reviewers. The research was supported by the MVZ and National Science Foundation IOS-090353 to R. Prum.
