Why Do Roosters Crow? The Clock Says When, Rank Says Who

Roosters that went 14 days without a sunrise kept up their predawn crowing anyway, on a near-24-hour rhythm that only slowly weakened. They lived in groups of four at Nagoya University, each bird in its own cage, in a light-tight, sound-tight room under a constant dim glow of less than 0.1 lux. In each group, the top-ranked rooster almost always crowed first.

The usual explanation for crowing is the sunrise. The study, published in Scientific Reports in 2015, found two things running the dawn call instead: a clock inside each bird, and the pecking order.

Why do roosters crow?

Roosters crow to claim territory and advertise their status, to rivals and to their own group. The call is inherited from the wild red junglefowl, the chicken’s ancestor. The dawn timing comes from an internal circadian clock rather than the sunrise itself, and in a lab study of roosters kept together, the top-ranked bird crowed first almost every morning.

The first crow comes two hours before the light

In 2013, Tsuyoshi Shimmura and Takashi Yoshimura reported in Current Biology that roosters kept on 12 hours of light and 12 of dim light began crowing about two hours before the lights came up, a habit National Geographic’s report says wild red junglefowl share. Under dim light around the clock for 14 days, the birds ran on a 23.7-hour day and crowed when they judged dawn was due, though the pattern gradually faded over the fortnight.

A rhythm that keeps going once every outside time cue is gone is called free-running, the mark of an internal clock. The 2015 paper reanalysed the same birds by rank and gave a finer figure: predawn crowing began an average of 1 hour 50 minutes before the lights came on. People carry the same kind of timer, and its mid-afternoon dip, which can arrive without any lunch, is one reason turkey takes the blame for a sleepy Thanksgiving.

The sunrise explanation runs in the wrong order

The popular story has the rising sun waking the rooster and the rooster answering it, a reasonable farmyard guess that gets the first crow wrong. Light can trigger a crow, but the crowing starts before any light arrives and keeps a near-24-hour rhythm when the light never changes.

The sun also works through the clock. The daily cycle of light and dark is “the most effective synchronizer for the circadian clock”, in the 2015 paper’s words, so sunlight sets the rooster’s clock and the clock sets off the crow.

Outside prompts are why a rooster seems to crow all day: light or another rooster’s crow can set him off at any hour, though “the crowing was mostly induced in the morning,” Yoshimura told ABC Science. He said the findings suggest the clock regulates a rooster’s sensitivity to outside cues as well as when he crows.

The top rooster crows first and the rest wait

Chickens in small groups form a linear, fixed pecking order, and the 2015 study found it carries over to the dawn call. Across three groups of four inbred roosters, the top-ranked rooster started the crowing on 97.6% of mornings. The others followed within a few tens of seconds, in descending order of rank.

With the top bird removed, the second-ranked rooster crowed first 92.7% of the time, though a lower-ranked bird sometimes got in ahead. The authors suggest the new leader was less able to hold the others back.

The subordinates can crow: prompted by light or a recording of crowing, they crowed as much as the leader did. What he held down was their predawn crowing, while each subordinate’s clock kept its own time: body-temperature rhythms differed from bird to bird even as the crowing stayed in step.

The lower-ranked roosters, the 2015 paper concludes, “are patient enough to wait for the top-ranking rooster’s first crow every morning and thus compromise their circadian clock for social reasons.”

A 2025 study by Dominic Wright and colleagues in Philosophical Transactions of the Royal Society B notes that the main indicator of a rooster’s rank appears to be “the frequency with which a male crows, not the composition of the actual call”. A spotted hyena’s giggle works the other way, carrying rank in how variable its notes are.

The crow is a territory claim kept from the junglefowl

The same study describes crowing as “the main territorial announcement of the ancestral red junglefowl” and “a reliable indicator of the status, size and health of the emitter”. A wild junglefowl group typically holds a small territory around a roosting tree, and the males announce its borders with loud crowing, “emitted mainly during dawn and dusk”.

Domestication, a gradual slide from red junglefowl to chicken, kept the call and edited it. The study’s domestic White Leghorns had a longer, lower last syllable than red junglefowl recorded in northern India, with more formants, the resonance peaks in a call’s sound.

Junglefowl kept captive in Sweden for many generations had last syllables as long, though, so the study cannot pin the change on domestication alone. Deliberate breeding goes further: some of Japan’s long-crowing chickens, the Naganakidori breeds such as Koeyoshi and Tomaru, can hold a single crow for more than 15 seconds.

Testosterone switches the crow on

Crowing depends on testosterone, which is why it belongs to roosters. “Although both sexes have the capacity to crow, typically only the male does,” writes the University of Kentucky’s Jacquie Jacob for the Cooperative Extension poultry site. In a 2019 Nagoya study, male chicks given testosterone implants grew prominent combs and began to crow.

The same team traced part of the switch to a midbrain region linked to crowing, the nucleus intercollicularis. There, testosterone turned up a gene for a receptor that responds to the hormone cholecystokinin, and chicks given gastrin, another hormone that activates the same receptor, crowed more often than chicks given saline. None of it has to be learned: a rooster develops the full ability to crow even if he is raised in isolation or surgically deafened from hatching.

His ear canal shuts when he crows

Crowing reached 142.3 decibels at the entrance of the rooster’s own ear canal in a 2018 study in the journal Zoology, as Phys.org reported.

Measurement	Sound level
At the entrance of the rooster’s own ear canal	142.3 dB
Half a metre from the rooster	102 dB
Level that can damage inner-ear hair cells almost at once	above 120 dB

Micro-CT scans of one rooster head and one hen head suggest part of how a rooster keeps his hearing. With the beak opened wide, the rooster’s outer ear canal closed completely while the hen’s only narrowed, and the authors think a bursa-like slit, more developed in roosters, is the reason. It is one of several protections: opening the beak wide also slackens his eardrum, and unlike people, birds can regrow damaged hair cells.

The rooster on the fence at first light has usually been at it for a while. A clock inside him started the crowing well before the light, the pecking order probably decided whether he went first if he had rivals, and his ear canal very likely shut each time he opened his beak to crow. The sun turned up last. Strictly FYI.