According to a trio of animal physiology researchers from Japan, the highest-ranking rooster has priority to announce the break of dawn.

The ‘cock-a-doodle-doo’ crowing of roosters, which symbolizes the break of dawn in many cultures, is controlled by their internal biological clock. When one rooster announces the break of dawn, others in the vicinity immediately follow.

Chickens (Gallus gallus domesticus) are highly social animals, and they develop a fixed hierarchy in small groups. Now, for the first time, scientists have demonstrated that the order of precedence of crowing in roosters is based on social ranking within the group.

Through observation of a group of four roosters, the team – Dr Tsuyoshi Shimmura from the National Institute of Basic Biology, Prof Takashi Yoshimura and Dr Shosei Ohashi from Nagoya University – found that there was a systematic rule in the order of crowing.

In addition, the starting time to crow for the dominant rooster varied from day to day, but the crowing of the lower ranking roosters always started right after the crowing of the highest-ranking rooster.

From these observations, the scientists identified that the most dominant rooster had priority to announce the break of dawn by being able to determine the timing to crow within the group.

“We found that when chickens were housed in small groups, the top-ranking rooster determined the timing of predawn crowing,” Dr Shimmura and co-authors wrote in a paper in the journal Scientific Reports.

“Specifically, the top-ranking rooster always started to crow first, followed by its subordinates, in descending order of social rank.”

Upon removing the highest ranking rooster from the group, the second ranking rooster became the first to crow, showing that the second ranking rooster can also take the role of the most dominant rooster.

“The presence of a dominant rooster significantly reduced the number of predawn crows in subordinates. However, the number of crows induced by external stimuli was independent of social rank, confirming that subordinates have the ability to crow,” the scientists wrote.

“We have discovered that roosters live in a strictly linear hierarchy, where social ranking reflects the order to announce the break of dawn,” Dr Yoshimura concluded.

_____

Tsuyoshi Shimmura et al. 2015. The highest-ranking rooster has priority to announce the break of dawn. Scientific Reports 5, article number: 11683; doi: 10.1038/srep11683