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.
Highlights
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
Sound transmission through the avian ear is influenced by the stapedius muscle, which was shown to react during self-generated vocalizations in the domestic chicken (Gallus gallus domesticus) based on electromyography measurements [8]
According to Ewald [10], the skin covering the lower jaw pulls on the skin of the ear canal due to beak opening, which in turn pulls on the tympanic membrane and changes its tension
Summary
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. Sound transmission through the avian ear is influenced by the stapedius muscle, which was shown to react during self-generated vocalizations in the domestic chicken (Gallus gallus domesticus) based on electromyography measurements [8]. Suggested explanations were muscle contractions in the outer ear, the insertion of air into the intracranial cavity via the pharyngotympanic tube or skull deformations during vocalization
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