Abstract
Courtship displays may serve as signals of the quality of motor performance, but little is known about the underlying biomechanics that determines both their signal content and costs. Peacocks (Pavo cristatus) perform a complex, multimodal “train-rattling” display in which they court females by vibrating the iridescent feathers in their elaborate train ornament. Here we study how feather biomechanics influences the performance of this display using a combination of field recordings and laboratory experiments. Using high-speed video, we find that train-rattling peacocks stridulate their tail feathers against the train at 25.6 Hz, on average, generating a broadband, pulsating mechanical sound at that frequency. Laboratory measurements demonstrate that arrays of peacock tail and train feathers have a broad resonant peak in their vibrational spectra at the range of frequencies used for train-rattling during the display, and the motion of feathers is just as expected for feathers shaking near resonance. This indicates that peacocks are able to drive feather vibrations energetically efficiently over a relatively broad range of frequencies, enabling them to modulate the feather vibration frequency of their displays. Using our field data, we show that peacocks with longer trains use slightly higher vibration frequencies on average, even though longer train feathers are heavier and have lower resonant frequencies. Based on these results, we propose hypotheses for future studies of the function and energetics of this display that ask why its dynamic elements might attract and maintain female attention. Finally, we demonstrate how the mechanical structure of the train feathers affects the peacock’s visual display by allowing the colorful iridescent eyespots–which strongly influence female mate choice–to remain nearly stationary against a dynamic iridescent background.
Highlights
Courtship displays often involve movements that stimulate multiple senses [1,2,3,4,5]
Courting peacocks perform the train-rattling display using a relatively narrow range of feather vibration frequencies between 22 and 28 Hz (Fig 3), and yet within that range we found that different individuals use relatively consistent vibration frequencies
What determines one peacock’s ability to perform higher frequency vibrations than another? We analyzed data from a limited number of individuals to investigate whether variation in train morphology constrains vibrational frequency, and found that adult peacocks with longer trains shook their trains at slightly higher frequencies on average (Fig 3B)
Summary
Courtship displays often involve movements that stimulate multiple senses [1,2,3,4,5]. A courting peacock will raise his tail and train feathers (Fig 1A), and often vibrates those feathers once the peahen is in front of him [14]. This “train-rattling” display attracts the peahen’s visual attention [15] and always precedes copulation [14]. Most of the train feathers have a single eyespot at the distal end, and peacocks that display eyespots with greater iridescence obtain more matings [11, 12], whereas natural variation among peacocks in train length and the number of displayed eyespots is not associated with mating success [10]
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