I have been shaken and inspired by the earthquake of yesterday.
As reported in the study by C.P.H. Elemens et al., in vivo electric potential measurements from syringeal muscles of Zebra Finches and European Starlings were found to be in phase with frequency modulations of song in excess of 200 Hz. In situ muscular stimulation produces frequency modulations in song. Furthermore, based on in vitro stimulation and response measurements, there is sexual dimorphism in Zebra Finch syringeal muscle performance as female muscle contraction time was found to be nearly twice that for male syringeal muscle contraction. Starling syringeal muscle performance was found to be monomorphic.
Syringeal vibrations are not the only way to make some noise. High-speed video of the characteristic courtship “J-dive” of Anna’s Hummingbird reveals that the “chirp” is mechanical sonation by vibration of the vane of outermost retrices. Furthermore, vane flutter frequency was found to be highly correlated to sonation frequency in the study conducted by C.J Clark and T.J. Feo. By removing retrices or the trailing (inner) or leading (outer) edges of the outermost retrices, researchers demonstrated that sonation was disabled in males whose trailing edges of the outermost retrices had been excised. By wind tunnel experiments, they verified that vibration frequency of the trailing vane was 3.3-4.7 kHz. Sonation by retrix vibration was also found to be at the least nearly 20 dB louder than syrinx vocalization. Researchers have shared audio and visual supplements in the university’s press release. Also, there is mention of barbule linking barbs; more accurately, it is the barbicels linking barbules of barbs that would contribute to rigidity of the the vane. And contrary to the statement in the press release, removal of the leading vane of the outermost retrix did not completely disable sonation.
Copulation in birds is often described, especially in the case of songbirds, as a “cloacal kiss,” which appears to be a brief meeting of cloacas. In only 3% of birds, a phallus is observed. M. Rowe et al. in their study, have identified, in some species of Maluridae, a non-erectile muscular hydrostat at the tip of the cloacal protuberance. By histological analysis and optical microscopy, researchers characterized the appendage as a matrix of longitudinally oriented muscle fibre and connective tissue (e.g. collagen and elastin) having keratinised epithelium. Furthermore, among species in which mate-competition is more intense, or those in which extra-pair paternity rates are high, larger cloacal tips were observed. Despite the title the study, researchers did not verify that the this cloaca tip vibrates during or before copulation, but based on structure and muscle alignment, a single plane of motion is predicted.