Why do roosters crow in the morning? The obvious answer is that the sun comes up and tells them it is time to wake everyone else. But that is not quite how it works. Roosters have an internal circadian clock that tells them dawn is approaching. They start crowing before there is any change in the light, and they keep to that schedule even when the normal day and night cycle is taken away. Light, sounds and other disturbances can set a rooster off at other times, but its body clock decides when it is most ready to respond. And there is a twist: when several roosters live together, the highest-ranking bird gets to crow first.
Roosters know dawn is coming
People have linked roosters with sunrise for thousands of years, but it took until 2013 for scientists to test whether the birds were reacting to light or anticipating the time of day. Researchers Takashi Yoshimura and Tsuyoshi Shimmura at Nagoya University in Japan kept roosters on a schedule of 12 hours of light and 12 hours of darkness. Even though the lights did not come on until the start of the “day”, the birds began crowing two to three hours beforehand, as the ABC reported at the time. That was the first clue that something other than morning light was setting the timing.
The researchers then took the light and dark signal away completely by keeping the birds in constant dim light. The roosters still crowed on a daily pattern. As The Naked Scientists explains, the birds crowed a little earlier with each passing day, and Scientific American puts the cycle at 23.7 hours. That steady drift is exactly what you would expect from an internal clock running without an outside time signal to correct it. The study, published in Current Biology, concluded that predawn crowing is controlled by a circadian clock, the same kind of daily rhythm that governs our own sleep, which I wrote about in what is a circadian rhythm? In other words, the rooster is not looking at a brightening sky and deciding morning has arrived. Its body clock has already been counting down.
Light can still set a rooster off
That does not mean light has nothing to do with it. The same research showed that outside triggers, such as a sudden light or the sound of another rooster, can make a rooster crow. The important detail is timing. The birds were far more likely to respond to those triggers around the time their internal clock expected dawn, and The Naked Scientists notes that when the same triggers were used in the middle of the night, the roosters did not crow at all. The clock effectively sets how sensitive the bird is to its surroundings, which explains why a rooster might crow when car headlights sweep across the yard or another rooster starts up, but does not react the same way at every hour of the night. The clock sets the stage, and the outside world provides the cue.
The boss rooster gets the first call
The story gets better when several roosters share a yard. In 2015, the same Nagoya team studied groups of four roosters and found a remarkably consistent pattern. According to the study’s abstract in Scientific Reports, the top-ranking rooster always started the predawn crowing, followed by the others in descending order of rank. When the researchers removed the top bird, the second-ranking rooster took over the first call. The dominant bird’s presence even reduced how often the lower-ranked roosters crowed before dawn.
The lower-ranked birds were perfectly capable of crowing first. When the team set off crowing with light or sounds, the subordinates crowed just as much as the boss, as the research announcement on EurekAlert explains. They simply waited their turn every morning, putting their own body clocks on hold for social reasons. So the dawn chorus is not four birds waking up at roughly the same time; the pecking order decides who speaks first.
Why roosters crow at all
Crowing is far more than an alarm clock. It is a social signal that advertises a rooster’s presence, helps establish and defend territory, and reflects where he sits in the pecking order. That is why roosters crow during the day too, in response to another rooster, a disturbance or a perceived threat. The morning is simply when the circadian system makes them most ready to crow. It also explains the classic image of a rooster calling from the highest point he can find; a higher perch helps the sound carry further across the surrounding area.
Loud enough to need earplugs
And it carries a long way, at least up close. In a 2018 study, researchers from the Universities of Antwerp and Ghent in Belgium measured sound at the entrance of roosters’ ear canals while they crowed and recorded levels as high as 142.3 decibels, as Phys.org reported. That figure needs context, because it was measured right at the bird’s ear, not across the yard. Discover notes that even the loudest crow had dropped to about 100 decibels at 50 centimetres. Still, it raises an obvious question: how does a rooster avoid damaging its own hearing?
The answer is mechanical. Using micro-CT scans, the researchers found that a rooster’s outer ear canal closes when the bird opens its beak, and when it tilts its head back to crow, a piece of soft tissue covers the canal completely, like a built-in earplug. Hens have a similar structure, but their ear canal only narrows rather than closing fully, and their calls are far quieter anyway, at around 70 decibels. Birds also have an advantage we lack: they can regrow damaged hair cells in the inner ear. It is a neat example of anatomy shaped around a behaviour that would otherwise cause a serious problem, and hearing turns out to matter enormously in the animal world, as my post on echolocation shows.
Why most Australian backyards are rooster-free
There is also a very practical reason you may not have a rooster next door: local laws. In Brisbane, for example, Brisbane City Council lets residents keep chickens and other poultry with a free self-assessed permit, allowing up to six birds on a block smaller than 800 square metres and up to 20 on a larger one, but roosters cannot be kept in a residential area at all. Other councils set their own rules, and they vary widely; the City of South Perth, for instance, also prohibits roosters, as a round-up of council rules from Backyard Chicken Coops shows. So if you are thinking about starting a backyard flock, do not assume a rooster is allowed just because hens are; check your own council’s current rules first.
So the familiar sound outside your window is the product of several things working together: a body clock that prepares a rooster to crow before dawn, a pecking order that decides who goes first, a territorial message aimed at every other rooster within earshot, and a voice so loud the bird needs its own earplugs. It may sound as though the rooster is announcing that morning has arrived, but really, it knew morning was coming before the sun did.
Sources
- ABC Science: Roosters cock-a-doodle-doo by the clock
- The Naked Scientists: Clock-a-doodle-doo
- Scientific American: Internal clocks tell roosters it’s crow time
- Shimmura, Ohashi and Yoshimura: The highest-ranking rooster has priority to announce the break of dawn, Scientific Reports (2015), abstract
- EurekAlert: Bossy cock takes the lead vocal of cock-a-doodle-do
- Phys.org: Why roosters don’t go deaf from their own loud crowing
- Discover: Roosters have special ears so they don’t crow themselves deaf
- Brisbane City Council: Chickens and poultry
- Backyard Chicken Coops: Will my council allow me to keep chickens?