My grandmother knew the sounds of the farm, and there were many. Some her family counted on to begin the day, like the rooster's crow. Most people think the sun or the break of light cutting through the darkness tells the rooster to sound off. But many roosters crow while it's still dark. How then do they know it's time to sound off? ​ Roosters, like humans, have internal time mechanisms, i.e., a biological clock known as a circadian rhythm. This clock tells when to wake up,