National Geographic News
A rooster crows in the Andes in Peru.

A rooster crows in a deforested Amazon cloud forest (file picture).

Photograph by Gordon Wiltsie, National Geographic

Jane J. Lee

National Geographic News

Published March 18, 2013

Back before alarm clocks jolted us awake to greet the morning with bleary-eyed confusion, roosters performed that daily duty. Now, a new study shows that roosters don't need the light of a new day to know when it's dawn—rather, their internal clocks alert them to the time.

While researchers at Nagoya University in Japan were studying the genetic underpinnings of innate vocalizations—or nonlearned behaviors such as crowing—in chickens, they discovered that the male birds don't need external light cues to know when to start crowing. (Also see "Night Owls Stay Alert Longer Than Early Birds.")

"To our surprise, nobody [has] demonstrated the involvement of the biological clock in this well-known phenomenon experimentally," study co-author Takashi Yoshimura, who specializes in biological clocks at Nagoya University, said in an email.

Shedding Light on Roosters

During their experiments, Yoshimura and colleague Tsuyoshi Shimmura, also of Nagoya University, put PNP roosters—an inbred strain of chickens used often in laboratories because of their genetic similarities—through two different light regimens.

In the first experiment, roosters experienced 12 hours of light and 12 hours of dim light conditions for 14 days. The scientists found that the roosters would start to crow two hours before the onset of light—called anticipatory predawn crowing—consistent with observations in wild red jungle fowl. (See National Geographic's pictures of game birds.)

In the second experiment, roosters were kept under 24 hours of dim light conditions for 14 days. Yoshimura and Shimmura noticed that the animals started running on a 23.8-hour day and would crow when they thought it was dawn, according to the study, published March 18 in Current Biology.

When the scientists exposed the roosters to sound and light stimuli to test whether external cues would also elicit crows, they found that the animals would vocalize more in response to light and sound in the mornings than during other times of day. This means the roosters' internal clocks take precedence over external cues.

The researchers also found social rank among the birds affected the timing of when they crow.

"Crowing is a warning signal advertising territorial claims. Our preliminary data suggest that the highest ranked rooster has priority in breaking the dawn, and lower [ranking] roosters are patient enough to wait and follow the highest ranked rooster each morning," said Yoshimura.

Rooster Study a Long Time in Coming

Kristen Navara, a hormone specialist in poultry at the University of Georgia in Athens, said she isn't sure why no one has taken a closer look at this phenomenon before. (See pictures of rare chickens in National Geographic magazine.)

"I think many times we don't think to study what appears right in front of us," Navara, who wasn't involved in the research, said by email.

For instance, "we have definitely noticed in our own roosters that they begin to crow before dawn and have wondered why that was, but just never thought to test whether it was a circadian rhythm driven by an internal clock rather than an external cue."

Added Navara, "I think this is a very interesting study and something that should have been done a long time ago."

9 comments
Deb Matteson
Deb Matteson

I don't know why this question came to me,  but,  it's a really cool and just accepted phenomenon.  Just one of those things that you realize but never question. 

mbhsbj ahbdf
mbhsbj ahbdf

Yes, this study is interesting to me as well, and I think there are more conclusions to be drawn.

Also, it might not be true to assume that anything similar has not been done in the past. It's safer to say that such studies are not found in documented reports that are available to us.

Barbara L.
Barbara L.

Okay, researchers answer this for me:  how does my dog know exactly what time I need to get up -- she begins by licking my ears ...

Jay Arr
Jay Arr

We raised chickens when I was growing up, and I can say from lots of experience that our roosters tended to crow when- and where-ever they so chose, regardless of time of day or night.  We had one big old golden Sex Link rooster that crowed off and on all night long for years.  And of course, any time the other roosters thought they could crow, he'd chase them around like a schoolyard bully... they still got to crow, but they got lots of exercise thereafter too.  lol :)

jim adams
jim adams

I grew up with roosters around and have raised egg chickens (with roosters) for the last 20 years,.  I note that roosters crow on somewhat differing schedules.

Let's start earlier.  Chickens are among the most night-blind of animals.  They start going to roost an hour to half an hour before sunset. It's  dark to chickens when it is dusk to us (they walk like they can't see well). The reverse is true in the gloaming of the morning... they come out into the day well after song birds are hopping around in the grass under our bird feeder. In the times of the long nights (winter), when night stretches to 14 hours, roosters may start crowing at 2 a.m. --sometimes a bit earlier, more often a bit later


I notice for myself that i wake up when i can't sleep any more ,, even if i try to. I whimsically say "my sleep reservoir is empty". It may not be true, but it sure is what it feels like.  

So, i see no behavioral regularity which i could call a "biological clock". Crowing varies an hour or three according to the kind of rooster and the length of night. Bored roosters crow earlier than non-bored roosters -- house chickens or yard chickens vs pastured chickens.  Me? i think their sleep reservoir is empty, and a bored, night-blind, non-sleepy rooster uses the only word in his vocabulary to say so

 Which of course raises the question: how in the blazes to such noisy animals survive in the wild. The rooster announces to the world "I'm here, I'm here!!!" and when a dominant hen lays an egg, the whole flock announces: "I laid an egg, I laid an egg", "She laid an egg, She laid an egg." How DO they survive in the wild?

First Last
First Last

Apparently the researchers aren't aware of those roosters who crow during the night.

Rent Strike
Rent Strike

Poor roosters! Locked up in a lab so that people can study such a thing. Instead of running this pretty picture of a rooster in nature, NatGeo should be honest and show us caged birds in a vivisection lab.

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