Just before dawn, even before the sun appears in the eastern horizon, rooster always crowing. Apparently, according to the research results, it is something to do with a natural daily rhythm rooster owned.
Rooster crowing because it has an internal clock that help him precedes the rising of the sun. As well as birds, roosters singing or crowing in the daily cycle.
Almost all animals have a daily cycle of activity known as circadian rhythms. It is a biological rhythms in animals, the cycle will be repeated each day and night.
Rooster precedes sunrise to start the daily hunt for food and also for the defense of the region. However, if a neighbor's rooster has an internal clock that is set up a little earlier, it may stimulate other roosters to crow early too. That's why sometimes roosters crow at night.
The crowing rooster at sunrise actually is a way to proclaim territory. When a rooster crows, it sends a signal to other roosters that if their territory violated, it means that they requested a fight.