Abstract
The “cock-a-doodle-doo” crowing of roosters, which symbolizes the break of dawn in many cultures, is controlled by the circadian clock. When one rooster announces the break of dawn, others in the vicinity immediately follow. Chickens are highly social animals, and they develop a linear and fixed hierarchy in small groups. We found that when chickens were housed in small groups, the top-ranking rooster determined the timing of predawn crowing. Specifically, the top-ranking rooster always started to crow first, followed by its subordinates, in descending order of social rank. When the top-ranking rooster was physically removed from a group, the second-ranking rooster initiated crowing. 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. Although the timing of subordinates’ predawn crowing was strongly dependent on that of the top-ranking rooster, free-running periods of body temperature rhythms differed among individuals, and crowing rhythm did not entrain to a crowing sound stimulus. These results indicate that in a group situation, the top-ranking rooster has priority to announce the break of dawn, and that subordinate roosters are patient enough to wait for the top-ranking rooster’s first crow every morning and thus compromise their circadian clock for social reasons.
Highlights
The “cock-a-doodle-doo” crowing of roosters, which symbolizes the break of dawn in many cultures, is controlled by the circadian clock
When we looked at temporal changes in the incidence of predawn crowing in detail, subordinates followed the top-ranking rooster within a few tens of seconds (Fig. 1e)
We discovered that the highest-ranking rooster crows first every morning, followed by its subordinates in descending order of their social rank (Fig. 1c–e)
Summary
The “cock-a-doodle-doo” crowing of roosters, which symbolizes the break of dawn in many cultures, is controlled by the circadian clock. The timing of subordinates’ predawn crowing was strongly dependent on that of the top-ranking rooster, free-running periods of body temperature rhythms differed among individuals, and crowing rhythm did not entrain to a crowing sound stimulus These results indicate that in a group situation, the top-ranking rooster has priority to announce the break of dawn, and that subordinate roosters are patient enough to wait for the top-ranking rooster’s first crow every morning and compromise their circadian clock for social reasons. Bird to recognize the others (generally, less than 10 individuals), chickens develop a linear and fixed hierarchy, known as the “pecking order”[11,12] In such groups, the behaviors of each rooster reflect the social hierarchy, and higher-ranking roosters have priority for food, mating, and resources in the pen such as nests and roosting places[8,13]. We show that the top-ranking rooster has priority to determine the timing of predawn crowing, and that subordinates are obedient to the top-ranking rooster in a group situation
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