Its basically to let everyone know whose turf it is. They crow to let the girls know they are there, they crow when they see someone or something new come in their turf, they crow to send a message ect. Roosters are vocal and crowing is their way of sending their point across to whomever and whatever is around.
I raised some peeps in my greenhouse before the new coop was built. Yup. When the moon was full and round, and the night was clear and crisp all 8 roosters would crow all night long............................................
Buckles seems to have a built in alarm clock. I let them out to free range for an hour each night and stay with them because there are kazillions of hawks around. When it is about time for me to let them out of their coop he starts to crow. I am at the point still inside the house so I guess he is trying to remind me?
My largest Roo would crow when he heard me coming. None of the others have yet. We just had to cull the Roos the hens didn't prefer. I already miss his calls of good morning. :-( I'm hoping one of the remaining will learn to crow.
He's trying to make his territory known. Notice that the crows do vary. Sometimes the crow is to warn the hens of danger (that's when you see the hens running in a panic). I have a stupid bantam that crows in the middle of the night.
Time to get up ~ at least that's what mine does. He crows the minute the sun comes up!! He roosts outside my downstairs bathroom window, so if I wake up in the middle of the night and turn on the light, he will crow. When he see's me driving up in my truck he runs to the driveway side and crows (this one is my favorite) He also crows back and forth to other roosters in the neighborhhood, I have on to the north of my house and one to south.
My guess would be establishing his territory, calling to a mate, announcing good new and bad news - alarms. That's how done birds use their calls. I don't think chickens are that different with their vocalizations. I want to say I've heard of someone who studied chicken sounds at great length and found they have lots of different sounds. Almost like their own language. Crowing is just an exclamation point.
OMG...rooster has been up for 4 hours crowing. The moon is right outside my house shining past the tree so he can see it from his roost spot. I even sat out there with him, but nooooo...my neighbors are gonna kill me, note to self: give neighbors food from garden today!! ")
He started at three in the morning and was non stop till eight am....I tossed him a couple of frosted mini wheats and he cackled tapped his nose to his water dish, as if fill it........he shut up after that. He has never done that. Personally, he has been acting so weird lately, I think he wants to mate.