By David Manly
Apr. 22, 2013 – A signature sound of the farm is the rooster crowing as the sun rises to announce the start of the day. But why does the rooster crow? And how does he know when is the right time to do so?
Researchers at Nagoya University in Japan discovered that male birds do not need light cues in order to start crowing, but seem to “know” when it is the right time.
According to Dr. Takashi Yoshimura, who co-authored the study published in Current Biology, the crow itself is not a learned vocalization like human speech, but a more innate and natural sound that is controlled genetically (like a dog bark or a cat meow).
“We believe that chickens provide an excellent model for understanding this mechanism and we are now analyzing the genetic basis of rooster crowing,” said Yoshimura.
During the course of their experiments, the researchers determined that crowing is not controlled by the presence of light, but by an internal mechanism. The mechanism is known as a circadian clock – a biochemical process that alternates between day and night cycles approximately every 24 hours and causes changes in behaviour, such as in sleeping and feeding patterns.
“To our surprise, nobody demonstrated the involvement of biological clock in this well-known phenomenon experimentally,” added Yoshimura.
The experiment used a specific breed of rooster known as PNP, which were inbred and used in order to make all the test animals as similar as possible. Four of the animals were placed together, since roosters do not crow in isolation, in a light and sound-tight room and recorded experiencing 12 hours each of light and dim light conditions. The results showed that the animals did not crow as light broke, but a few hours earlier.
“The roosters usually crowed 2 or 3 hours before the sunrise (when it is still dark) under normal 24-hour cycle. We call this “anticipatory predawn crowing,”” he said.
In a secondary experiment, the researchers kept the roosters under 24 hours of dim light, and discovered that the animals internally adjusted their internal clocks to a slightly shorter day, approximately 23.8 hours. This caused what Yoshimura called “free-running rhythm of crowing” – the roosters crowed when they thought it was dawn, approximately 10-15 minutes earlier every day under dim light conditions.
The next step in Yoshimura’s research is to identify the specific genes regulating rooster crowing, which is traditionally viewed as a warning signal advertising the males territory, as well as helps to determine social ranking.
Added Yoshimura, “Interestingly, our preliminary data suggest that the highest-ranked rooster has priority in breaking the dawn, and lower-ranked roosters are patient enough to wait and follow the highest-ranked rooster each morning.”