Cockerels have built-in clocks

According to scientists in Japan, cockerels don’t crow at the break of daylight each morning, but instead a highly intricate circadian rhythm dictates when the bird lets rip. This discovery was made when a group of roosters were put in a soundproofed, windowless room and subjected to 24 hours of artificial lighting. Despite the continuous light, the roosters began crowing just before dawn the following morning, despite being unable to see the Sun rising.