Rooster Wake-Up Call? Cock-A-Doodle-Doo Driven By Fowl's Internal Clock, Say Scientists

Roosters do generally crow mostly just before the dawn, but they can also be set off by other things, like car headlights or the sound of other roosters.

For years, it has been “unclear whether crowing is under the control of an internal biological clock, or caused by external stimuli,” Nagoya University researchers Tsuyoshi Shimmura and Takashi Yoshimura wrote in a paper appearing Monday in the journal Current Biology.

According to Shimmura and Yoshimura's paper, the rooster's internal clock is primarily what times its crowing, though this rhythm can be influenced by external factors.

To determine whether light cues or circadian rhythms (a regular, 24-hour cycle of activity) are the primary reason behind a rooster’s crow, the scientists examined how often roosters crowed under different light cycles. One group of roosters was subject to 12 hours of light and 12 hours of dim light; another group was kept under constant dim light conditions.

Sound and video recordings were made of the birds 24 hours a day, making it easy to distinguish crowing from other everyday chicken noises.

Roosters kept on the 12 hours of light, 12 hours of dim light cycle crowed about two hours before lights came on. The roosters kept under constant dim light still adhered to a constant crowing schedule, nearly once every 24 hours. This strongly suggests there is some internal clock mechanism keeping the roosters crowing on time -- otherwise, one would expect the roosters kept in 24-hour dim light conditions to crow erratically.

The birds that were kept under constant dim light did eventually start crowing out of sync with the daily cycle -- probably thanks to being in unnatural light conditions that created a mismatch between their environment and their innate circadian rhythms.

However, the scientists were able to put the roosters back on schedule by administering testosterone, which is known to play a role in crowing behavior. It's similar to how late-shift workers or people with circadian rhythm disorders take supplements of melatonin -- a hormone produced in response to light and dark cycles -- to try and get their sleep cycles back in line. The addition of a substance that's been unnaturally depleted by odd living conditions "rewinds" the inner clock.

Shimmura and Yoshimura also saw that roosters crowed immediately after lights were turned on. Through other experiments, they found that the brighter the light that shined over a 30- minute period, the more the roosters crowed. The sounds of other roosters crowing also pumped up the birds' cackles.

But, importantly, the roosters' responses to light and sound were even stronger earlier in the day. So while the rooster's crow can be prompted by external factors, the innate circadian rhythm seems to be a fundamental driver of crowing.

“Our observations prove that the rooster breaks the dawn every morning as a function of his circadian clock,” the researchers said. “It has been known for a long time that crowing is also induced by external stimuli. We conclude that not only anticipatory predawn crowing, but also external stimulus-induced crowing, is under the control of a circadian clock.”

Unlike other bird songs, the rooster’s crow is an instinctive reaction, not a learned habit. Shimmura and Yoshimura are particularly interested in these kinds of innate vocalizations.

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

SOURCE: Shimmura et al. “Circadian clock determines the timing of rooster crowing.” Current Biology 23: R231-R233, 18 March 2013.