Even if you’ve never actually heard a rooster crow, you’re likely familiar with an old adage—that a rooster’s crow heralds the impending sunrise. To a certain degree, that’s true. Similar to other birds, roosters actually have an internal clock that helps them anticipate the sunrise. But the rooster’s crow serves a greater purpose than mere early-morning buzzer. In fact, it’s an action that’s deeply rooted in adversarial Darwinism.
Basically, those ear-splitting caw-caws serve as a warning shot, a way for a rooster to establish its territory with the morning light. By crowing, a rooster is warning other roosters not to trespass—or else.
This internal clock was discovered by researchers at Nagoya University, in Japan, who found that, when exposed to light and darkness in 12-hour increments, a rooster could always anticipate the lit hours, crowing approximately two hours before the darkness period ended. In their paper—which was published in the journal Current Biology—the researchers noted that roosters didn’t require the presence of sunlight to know that the sunrise is coming.
What’s more, the researchers also found that roosters with a higher social rank crowed first. Younger crows, often of a lower social rank, would patiently wait to send out their crows until after they had heard the calls of the other roosters. The operating theory, here, is that roosters in auditory proximity to each other will use sound to stake territorial claims. Roosters lower on the pecking order—smaller, weaker, younger—have to wait their turn.
The intrinsic need to establish territory is also why roosters will often climb to higher ground to crow, as they have a better vantage point in order make sure that no other roosters trespass on their marked territory. Also, on higher ground, the rooster’s crow can travel much farther, allowing more roosters to hear and heed their warnings.
However, despite the antagonistic evolutionary purpose behind this cawing, roosters can also help each other to stay on top of their internal clock and cawing schedule. (To be clear, it’s not a purposeful action.) For instance, if one rooster’s internal clock is set slightly before the sunrise, it can stimulate other surrounding roosters to crow just as early. On the other hand, if one rooster’s internal clock is set to slightly after the sunrise, the crow of other roosters will help them get back on track. In other words, yes, a rooster has an internal clock. But, in the event that it fails, the caws of other roosters serve as a failsafe—an external clock, kind of like how you or I would use an alarm clock.
Frankly, the extra sleep is preferable.
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