The rooster and sunshine I would say was their wake up call.
The biological clock is what everyone has.
You could do an experiment. In bed before falling a sleep tell yourself that you have to wake up certain time, repeat it to yourself a few times and you would wake up when you should.
sometimes i do this. For example, when I want to wake up at 8 in the morning, by setting up the biological clock I wake up at 07:59 exactly 1 minute before actual time. :)