Meeting Abstract
Courtship displays involving exaggerated ornaments are often costly and may serve as signals of male motor performance, a sign of male quality. To evaluate both the costs and signal content of these displays, we need to understand their underlying biomechanics. We used a combination of high-speed field video recordings, in vitro experiments, and detailed studies of feather morphology to describe how peacocks generate a coordinated audiovisual courtship display involving their large elaborate train. Peacocks were found to court females by vibrating their trains at remarkably consistent frequencies ranging from about 24-27 Hz, driven by the tail feathers strumming against the elongated tail covert feathers. Field recordings show that this stridulation produces coherent motion of the green feather barbs that form the visual background, as well as a broadband pulsating acoustic signal with harmonics at 26 Hz and 52 Hz. The peacock’s display frequencies fall within the range for optimal detection of both visual flicker and acoustic signals found for other bird species. This display frequency is also higher than expected given the scaling relationship between vibrational frequency and body mass found for other bird and mammal shaking behaviors, suggesting that the peacock’s display is an extreme motor behavior. To understand how peacocks are able to achieve coordinated motion of an array of feathers with the >160 multicolored eyespots remaining nearly stationary, we measured the resonant vibrational spectra of peacock tail and eyespot feathers. Our results demonstrate that peacock eyespot feathers achieve a novel scaling of frequency vs. length, with biomechanical properties that facilitate the performance of this extreme display.
