Sound attenuation in the ear of domestic chickens (Gallus gallus domesticus) as a result of beak opening

Abstract

Because the quadrate and the eardrum are connected, the hypothesis was tested that birds attenuate the transmission of sound through their ears by opening the bill, which potentially serves as an additional protective mechanism for self-generated vocalizations. In domestic chickens, it was examined if a difference exists between hens and roosters, given the difference in vocalization capacity between the sexes. To test the hypothesis, vibrations of the columellar footplate were measured ex vivo with laser Doppler vibrometry (LDV) for closed and maximally opened beak conditions, with sounds introduced at the ear canal. The average attenuation was 3.5 dB in roosters and only 0.5 dB in hens. To demonstrate the importance of a putative protective mechanism, audio recordings were performed of a crowing rooster. Sound pressures levels of 133.5 dB were recorded near the ears. The frequency content of the vocalizations was in accordance with the range of highest hearing sensitivity in chickens. The results indicate a small but significant difference in sound attenuation between hens and roosters. However, the amount of attenuation as measured in the experiments on both hens and roosters is small and will provide little effective protection in addition to other mechanisms such as stapedius muscle activity.

Do high sound pressure levels of crowing in roosters necessitate passive mechanisms for protection against self-vocalization?

“…However, the findings of Oeckinghaus and Schwartzkopff (1982), that attenuation is frequency dependent, may imply that less attenuation is present at higher frequencies in chickens. This implies that, despite the passive attenuation found by Claes et al (2016) and measured by Muyshondt et al (2017) and if the above reported SPL at the level of the rooster's head are confirmed, the sound pressure reaching the inner ear still remains close to the threshold level at which immediate damage can, potentially, be caused. Even if active protection by reflexive stapedius activation occurs damage can still take place.…”

“…Recordings were made in a large outside enclosure to ensure free-field conditions. R1 recordings were used in Muyshondt et al (2017). The first 11 crows of each rooster were used to calculate the mean SPL for each time step.…”

“…Interestingly, however, this was not observed in hens suggesting that the effect of craniokinesis on the tympanic membrane in roosters represents a passive protective mechanism against loud self-vocalization. Ex vivo experiments by Muyshondt et al (2017) show that beak opening in roosters results in reducing the power transferred from the tympanic membrane to the inner ear by approximately half (3.5 dB), while in hens, beak opening barely affects the transfer. As mentioned earlier, attenuation by stapedius activity reaches a maximum of 20 dB at 800 Hz.…”

Shift down, look up: A test of the non‐linearity and fear hypothesis in a non‐vocal skink

“…Importantly, skinks are naturally exposed to sounds that contain both frequency shifts up and down. At our study site skinks routinely heard bulbul alarm calls (Fuong et al, 2014) and rooster's crows (a species that could eat them; Muyshondt, Claes, Aerts, & Dirckx, 2017) which contain rapid frequency changes both up and down. Skinks seemingly biased what they learned toward downshifts.…”

Morphological and biomechanical predictions of cranial kinesis in reptile evolution

“…Chickens (Galliformes), parrots (Psittaciformes), crows (Corvidae), pigeons (Columbidae), and finches (Fringillidae) have all been discussed in regard to their kinetic capabilities. The majority of these studies have largely consisted of ecomorphological observations (Bock 1964;Burton 1974;Hoese and Westneat 1996;Bock 1999;Homberger 2003;Claes et al 2017;Muyshondt et al 2017. )…”