Virtually, all animals follow daily cycles of activity known as circadian rhythms. Roosters have also this innate quality. What I have observed is that as soon as the rooster wakes up in day or night it crows and hearing its clarion crow other cocks also begin to crow. Almost all the birds can be heard chirping at the dawn or early morning but rooster's- crow is louder than other birds'. Which is why rooster's crowing is noticed.