2.5K views · 89 reactions | Roosters don’t need to set an alarm to tell them when it’s time to crow — their internal circadian clock lets them anticipate sunrise with remarkable accuracy. To us sleepy humans, it may seem like they all start crowing at once. But scientists have found that roosters follow a strict social hierarchy: only the top bird can issue the first cock-a-doodle-doo of the day! Red Junglefowl © Rick Bergstrom | BirdNote | Facebook