Why do roosters crow in the early morning ?

Suppose you were awake late in the night and so it was late to go to bed. At the dawn, you just dove deep in the sleep. At that vary moment, a hash caw sound penetrate through the sound sleep what you desired to have after the tiring day. I know how you feel. I had that feeling each and everyday until my neighbors... ( FORGET ABOUT THAT). That sound was of a rooster. Each day at dawn rooster warn other male roosters not to come near his hub. he wanna say this is mine. And this is done right after the first light of the day. And if u have a good light source you can trick the rooster to do the same thing. many early birds are there who also do same kind of sound.. but we rather call them tweeting.

https://www.youtube.com/watch?v=ISWKZCmRS34