Why roosters don't go deaf from their own loud crowing

January 30, 2018 by Bob Yirka, Phys.org report

A team of researchers with the University of Antwerp and the University of Ghent, both in Belgium, has uncovered the means by which roosters prevent themselves from going deaf due to their own loud crowing. In their paper published in the journal Zoology, the group outlines their study of the birds and what they found.

Anyone who has ever lived on a farm has heard the familiar sound of the crowing rooster (male chicken). Few likely realize, however, just how loud that crowing can be. In this new effort, the researchers sought to measure how loud the crowing is, and how the rooster avoids deafness from hearing itself every morning.

The team placed a tiny microphone near the ears of sample roosters to measure how loud the crowing would sound to them. They found it was louder than thought—averaging over 100 decibels, which is roughly the same as running a chainsaw. People who regularly use chainsaws without ear protection, it should be noted, go deaf over time due to damage to the tiny hair cells in the inner ear. Chickens of both genders also have such hairs in their ears, and the team wondered why they weren't damaged. To find out, they performed micro-computerized tomography scans on the skulls of the birds.

They discovered that half of the birds' eardrum was covered by a bit of soft tissue that dampened incoming noise. They also found that when the rooster tilted its head back to crow, another bit of material covered the ear canal completely, serving as a built-in ear-plug. Thus, for the rooster, it is as if someone were sticking their fingers in their ears while they are crowing. The researchers noted the birds also have another advantage—unlike humans, birds can regrow damaged hair cells. As for why the hens and chicks do not suffer hearing damage from the male crowing, though not mentioned in the research, it is well known that roosters tend to seek a vantage point offering maximum reach when they crow (away from the hens and chicks), making sure everyone within earshot knows that the hens that live there are his.

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Putting the Clock in 'Cock-A-Doodle-Doo'

Mar. 18, 2013 — Of course, roosters crow with the dawn. But are they simply reacting to the environment, or do they really know what time of day it is? Researchers reporting on March 18 in Current Biology, a Cell Press publication, have evidence that puts the clock in "cock-a-doodle-doo" (or "ko-ke-kok-koh," as they say in the research team's native Japan).

"'Cock-a-doodle-doo' symbolizes the break of dawn in many countries," says Takashi

Yoshimura of Nagoya University. "But it wasn't clear whether crowing is under the control of a biological clock or is simply a response to external stimuli."

That's because other things -- a car's headlights, for instance -- will set a rooster off, too, at any time of day. To find out whether the roosters' crowing is driven by an internal biological clock, Yoshimura and his colleague Tsuyoshi Shimmura placed birds under constant light conditions and turned on recorders to listen and watch.

Under round-the-clock dim lighting, the roosters kept right on crowing each morning just before dawn, proof that the behavior is entrained to a circadian rhythm. The roosters' reactions to external events also varied over the course of the day.

In other words, predawn crowing and the crowing that roosters do in response to other cues both depend on a circadian clock.

The findings are just the start of the team's efforts to unravel the roosters' innate vocalizations, which aren't learned like songbird songs or human speech, the researchers say.

"We still do not know why a dog says 'bow-wow' and a cat says 'meow,' Yoshimura says. "We are interested in the mechanism of this genetically controlled behavior and believe that chickens provide an excellent model."

http://www.sciencedaily.com/releases/2013/03/130318132625.htm