You may have heard that roosters crow when the sun comes up, but scientists at Nagoya University in Japan have discovered that roosters don’t even need to see the sun to know when to crow! Their internal clocks let them know when the new day is beginning. The scientists first exposed the roosters to two weeks of 12 hours of light and 12 hours of dim light. The roosters would begin crowing two hours before the light conditions began. In a second experiment, the roosters were kept under dim light for 24 hours a day for two weeks. The roosters began crowing at around the same time every day when they thought it was dawn.
Kristen Navara, a hormone specialist in poultry at the University of Georgia in Athens, had noticed that sunlight didn’t appear before the roosters began crowing. “We have definitely noticed in our own roosters that they begin to crow before dawn and have wondered why that was, but just never thought to test whether it was a circadian rhythm driven by an internal clock rather than an external cue.”