There's a reason roosters have been favored as natural alarm clocks ever since people first became farmers. Even before the light of dawn, raucous roosters sound the alarm, waking up every living thing around with their clamorous crow. Belgian researchers actually found that a rooster's crow averages more than 130 decibels for 1-2 seconds, which is about as intense as standing 15 meters away from a jet taking off. One of the three studied roosters was recorded crowing at more than 143 decibels, which is like standing in the middle of an aircraft carrier with jets whizzing by.
Previous research conducted by Japanese researchers led by Takashi Yoshimura found that roosters love to crow in the morning because it's primarily about announcing territory and where a particular rooster sees itself on the pecking order. Experiments revealed that the most dominant rooster was the one who would start the crowing off, which begins around two hours before first light. The birds must have an internal body clock that tells them when to crow -- and very loudly we have to add -- the researchers concluded.
All things considered, why doesn't the rooster go deaf from its own clamor? According to the researchers from the University of Antwerp and the University of Brussels, half the rooster's eardrum is covered in soft tissue that insulates it from the racket. Additionally, a quarter of the ear canal completely closes during crowing, as reported in the journal Zoology. This is quite convenient for the rooster but doesn't do much for all other nearby creatures with a decent pair of ears.
The researchers came to this conclusion after performing micro-computerized tomography scans which rendered 3-D images of the birds' skulls.
What this means is that a rooster can't actually hear the full intensity of its own crows, which might explain why they're so annoyingly loud. But even though the intensity of a rooster's crow diminishes with distance, one can only wonder why nature would evolve such an ability that risks deafening a nest, hens and chicks included.
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Bird biology offers some clues. Unlike mammals, birds (along with reptiles and fish) can regenerate the hair cells of the inner ear if they are damaged. Unfortunately, all sensorineural hearing loss is permanent in mammals, which includes humans, since the hair cells in the cochlea don't grow back. Some scientists, however, are attentively studying the hair cell regeneration process in chickens in the hope of curing hearing loss in human subjects in future. Until that happens, don't stay too close to roosters.