The top cock within a group always gets to herald the break of dawn. And after he goes, the rest of the roosters crow in order of descending rank, according to findings published in Scientific Reports this week. Crowing out of turn is a cock-a-doodle-don’t.

Roosters have been announcing daybreak for people since 2600 B.C. at least, but there’s still a lot that we don’t know about this phenomenon. Researchers recently discovered that their crowing mechanism is regulated by an internal biological clock. And we know that chickens are very social and that they develop these so-called pecking orders: Higher ranking birds have first dibs on food, mating, and resources like nests and roosting places. This dominance hierarchy starts with one chicken pecking all of the other chickens. Then the second dominant chicken pecks all of the chickens (except for the dominant chicken, of course). The least dominant chicken remains harmless. 

To investigate if social hierarchy has an effect on crowing, Nagoya University’s Tsuyoshi Shimmura and colleagues studied groups of four roosters, fully matured at 30 weeks old. They gave the roosters different colored leg bands, and then kept them in a group cage to determine hierarchy. The team recorded the winners and losers of every aggressive encounter, which ranged from chasing and threatening to aggressive pecking. The roosters were then placed into individual cages. 

According to the team’s observations, the highest-ranking rooster crows first every morning, and he’s followed by subordinate roosters in descending order of rank. The lead rooster determines the timing of pre-dawn crowing, and while this start time varies from day to day, lower ranking roosters always start crowing right after the crowing of the top rooster. When the top-ranking rooster was removed, however, the second-ranking rooster became the first to crow, suggesting that it is the top bird’s presence that suppresses the crowing of others. 

Furthermore, based on implanted data loggers, the team found that body temperature rhythms differ among individual birds. So because they have to wait for the top rooster’s first crow every morning, the subordinate roosters are actually compromising their circadian clock for social reasons. 

[Via Nagoya University]