Roosters crow in pecking order: study

Social ranking determines the order of crowing in roosters, with the highest ranking rooster's "cock-a-doodle-do" marking the break of dawn, scientists have found for the first time.
Researchers from The Institute of Transformative Bio-Molecules (ITbM) at Nagoya University in Japan found that there is a systematic rule based on social ranking that determines the order of crowing in roosters.
Although the subordinate roosters have the ability to crow, they have the patience to wait every morning for the most dominant rooster to crow before crowing themselves, researchers found.
In 2013, Tsuyoshi Shimmura and Takashi Yoshimura of Nagoya University reported in Current Biology that the rooster's crowing mechanism is governed by their internal biological clock.

Triggered by the first crow from a rooster, other roosters nearby also start to crow like a ripple effect. Crowing is considered to be an action by roosters to alert others of their territory.
In addition, chickens are known to be highly social creatures and develop a dominance hierarchy called pecking order when a small number of chickens forms a group.

This pecking order starts with the dominant chicken pecking all the chickens, the second dominant chicken pecking all the chickens apart from the dominant chicken and with the least dominant chicken remaining harmless.
The social ranking of roosters is strongly reflected in the actions within the groups, and the highest ranking rooster has been known to have priority in eating and mating.

Shimmura and Yoshimura have now discovered for the first time that the order of precedence of crowing in roosters is also based on social ranking within the group.
Through observation of a group of four roosters, Shimmura in Yoshimura's research group, currently an assistant professor in the National Institute of Basic Biology in Japan, found there was a systematic rule in the order of crowing.
They found that the highest ranking rooster among the group was always the first one to crow in the morning.
The crowing was followed by the second, third and fourth ranking roosters, which shows that roosters crow in descending order of their social ranking.

In addition, the starting time to crow for the most 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.
Researchers 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.
Upon removing the highest ranking rooster from the group, the second ranking rooster became the first to crow.
"We have discovered that roosters live in a strictly linear hierarchy, where social ranking reflects the order to announce the break of dawn," said Yoshimura, who led the research and is a principal investigator at ITbM.

The study is published in the journal Scientific Reports.