Why do roosters crow in the morning?

"The lights are on at midnight and the cocks crow at dawn, which is the time for men to study." I was born in the countryside. When the rooster crowed, it was time for my mother to wake me up. At that time, I really hated the crowing rooster and beat it up in private. But I also wondered why the rooster could wake up on time and be so energetic after waking up, but why I had to be woken up by adults and still be groggy after waking up?

Later I realized that the regular morning crowing of roosters is related to rhythm, which is also reflected in the content of the 2017 Nobel Prize.

(The 2017 Nobel Prize in Physiology was awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young for their discovery of the molecular mechanism of circadian rhythm)

However, the crowing of a rooster is also affected by light. Today, let's talk about what factors affect the crowing of a rooster?

01. Why do chickens crow in the morning?

Chickens can crow at different times and for different reasons. The most familiar one is the morning crowing. There were two theories in the past about why chickens crow in the morning.

1. Circadian rhythm. This theory believes that the main factor causing chickens to crow is more of an internal regulatory factor evolved from biological evolution, the circadian rhythm. In fact, from the appearance of life on Earth to the present, the sun has always been one of its biggest external factors, so the response to the sun will also be a basic process, thus forming a ubiquitous circadian rhythm problem, which exists in the form of genes.

2. Stimulus theory. Living things are responsive to stress, which is one of the basic characteristics of living things to maintain survival. As light is a very common stimulus in nature, it is normal for it to have an effect on chickens, just like the familiar phototaxis.

02. The influence of circadian rhythm

Which of the above two theories can better explain this phenomenon? So the researchers conducted an experiment. In fact, the experiment is not difficult. The core of these two theories lies in whether light stimulation is the key influence of crowing .

So they decided to study the effect of light, which is much easier for modern science. They controlled the light in a closed space, turning on the light for 12 hours (12L) and then turning off the light for 12 hours (12dimL). And this control also has the advantage of eliminating the influence of the earth's rotation and revolution, after all, the sunrise time is different every day.

Of course, this won’t work in the short term. They conducted an experiment for two weeks and the results are shown in the figure below.

After two weeks of regular light treatment, you can see that the roosters are not very punctual. They crow at different times, for example, some crow at 0, some crow during light hours, and sometimes crow during darkness.

But is there a maximum value for these crowing sounds? The answer is yes.

The main crowing time of the rooster is a little before the light starts , about 2 hours. Since this is an experimental environment, there will not be a gradual change in light in our natural environment.

Therefore, it can be concluded that the main influencing factor of crowing is rhythm rather than light .

03. Stimulus Effect

But does light really have no effect? ​​The answer is no!

In order to study this problem, the researchers decided to put the chickens in a state of complete darkness to see how the chickens would behave without light. The results showed that there was indeed an effect.

It manifests itself in two aspects.

First, the crowing cycle of chickens changed. The study found that as the experiment progressed, the crowing cycle of chickens changed from 24 hours to 23.8 hours, a difference of 0.2 hours.

Secondly, the rooster's crowing cycle has been disrupted. Although there is still a relative maximum, the frequency of crowing at other times has also increased.

From this we can see that light actually still affects the crowing of chickens.

04. What other factors may affect the crowing of a rooster?

So, are there other factors that influence the crowing of a rooster? For example, the sound? Just like the story of the rooster crowing in the middle of the night.

The answer is yes.

As shown in the figure above, we can see that sound stimulation also affects the crowing of chickens.

So, could hormones be a factor? The researchers decided to use capons for the study, capons vs testosterone implants, and found no significant difference, so testosterone should have no effect on the crowing of chickens.

It can be seen from this that the factors affecting the crowing of chickens are quite complex, including circadian rhythm, light, sound and other stimuli.

Everyone should know why chickens crow in the morning, but why chickens crow and the influence of other factors on crowing remain to be studied.

Shimmura, T., & Yoshimura, T. (2013). Circadian clock determines the timing of rooster crowding. Current Biology, 23(6), R231–R233.