Many in the cities go to bed at night with curtains drawn to shut off lights, and wake up when the alarm sounds. There are few environmental signals to tell us that it is morning. But go to villages and you wake up to the crowing of the cock. Records reveal that this has been happening since the Indus Valley days (3500 BCE). (Incidentally, the word cock is the short form of a cockerel, and when cockerel is part of a group of hens in the pen, it is called a rooster, as the word roost denotes a settled group.) While we normally use the word cock, scientists use the word rooster. Much research has been done on why the rooster crows. While the the crowing of roosters is described in Tamil as “kokkarako ko”, in English as “cock-a-doodle-do” and in Japanese as “Ko-ke-kok-koh”. Why they crow in the morning at day break has been the study of some bird scientists. While several theories had been debated, the actual answer is that it is due to the body clock (or circadian rhythm) of the rooster. This has been shown by a group of Japanese scientists led by Dr Tsuyoshi Shimmura of the Laboratory of Animal Physiology at the Nagoya University, Nagoya, Japan.
They recorded the crowing of a set roosters first using a 12-hour-full-light, 12-hour-dim light (12L: 12dimL) condition, and then under constant dim light (dim LL) condition. Under the (12L: 12dimL) condition, the roosters started crowing approximately 2 hours before the onset of sun light (sort of a pre-dawn crowing). But under the constant dim light condition (dim LL), it was a free running chatter, and this too had a period of 24 hours, but it damped off soon. Likewise when the researchers shone bright light from torches or car head lights, crowing occurred, but the crowing was weak and brief, and tapered off quickly.
Crowing Order and Pecking Order
Chicken are social animals, living in groups. When one rooster in the group crows at dawn, other roosters in the group join the chorus, though weakly and a bit later. It appears the crowing is a means of advertising their territories, so that no foreign wars start. As to why one rooster in the pen starts crowing first and the remaining roosters follow suit was also studied by the Shimmura group. They found that the one to crow first is the highest ranking rooster in the pack. He has priority to announce the break of dawn, the others are his subordinates. (Interested readers may access, < Scientific Reports /5:11683/Doi:10.1038/srep 11683>). He rules the roost.
The hens in the pen do not crow. They only chatter a bit and that too among themselves in the pack. There might be a social order amongst them too, establishing a “pecking order” just as the males have a “crowing order.” Do the hens too have a circadian clock built in them? Apparently so, particularly during ovulation and egg production. And as the male hormone peaks up at pre-dawn hours in a rooster, the hormone gonadotropin appears important during ovulation of hens. As to why hens only chatter while roosters crow so loud, the answer seems to lie in the differences in their anatomy.
Loud as a jet plane roar
How loud is the crowing of a rooster? This has been studied by a Belgian group. Using an instrument that measures the sound intensity, they found it to be as loud as what hits our ears when we stand next to a jet aircraft. Sound intensity is measured in units called decibels. The full-blown crowing intensity of a “king” rooster is as high as 143 db (that of a jet engine is about the same); of course this is when we are about a foot away. This level of 140 db can damage your ear drums and deafen you. Thankfully, it weakens in intensity as you move farther away from it. (Usually, the hens stay about a yard or a metre away).
For comparison, the loudness of a whisper is 30 db, a mosquito buzz 40 db and busy traffic 80 db, and the sound of a baby crying out loud can hit 100- 120 db. (My friend Jacob Tharu, who thought of naming his daughter Isabelle, changed his mind upon hearing the infant wailing loud, saying that the name decibel might suit her better! Her real name is Susanna). A sound of over 130 db can damage our ears.
With such a loud crowing, why does the rooster itself not become deaf? Kimberly Hickock, summarising the Belgian work, points out that their ears are specially built. The researchers strapped microphones to the rooster to their ears as it crowed. They found that their ears are blocked when they crow; a quarter of their ear canals completely close and soft tissue covers half of their eardrums; in fact, they do not hear their own crowing at full strength. Their skulls are also made so as to withstand this racket. The hens, with their inherent wisdom, stay about a yard or meter away, so that they are not affected with the sound; even if they did, their hair cells in the inner ear apparently quickly regenerates.
dbala@lvpei.org
