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.
"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."
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