Birds, with the exception of the Barn Owl, do not hear well at high frequencies. Chicken (hen or rooster), for example, have very sensitive hearing in the low frequencies but are limited to hearing sounds below 10 kHz. Given their sensitivity to low-frequency sound, one might wonder how a rooster that wakes up entire villages every morning with its crowing, keeps from losing its own hearing.
Knowing what we know about the mammalian auditory system, one might quickly suspect that the rooster utilizes run-of-the-mill tactics like the middle-ear muscle reflex to protect its own hearing while vocalizing. But that would be boring. Turns out that the rooster does in fact stiffen the middle-ear transmission chain during vocalization. However, this reaction is activated mechanically and not acoustically.
The middle-ear system is stiffened whenever the jaw is open thereby providing some protection when the rooster crows but not in response to other loud stimuli. The second interesting aspect of this mechanical middle ear reflex is that it only provides a few decibels of attenuation. So, the question remains. How does the rooster not lose its hearing over a lifetime of crowing. Here comes the interesting evolutionary twist. Turns out that jaw movement necessary for crowing also causes the rooster’s ear canal to collapse thereby providing another significant means of attenuation. In a recent paper, Claes and colleagues estimated this attenuation to be as many as 10s of dB. There you have it, crow away at the top of your lung capacity, but remember to close your ear canal.
Claes R, Muyshondt PGG, Dirckx JJJ, Aerts P. (2017) Do high-sound pressure levels of crowing in roosters necessitate passive mechanisms for protection against self-vocalization? Zoology (Jena) Dec 24.
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