Biology
The Role of Circadian Clocks in Seasonal Timing of Reproduction in Birds
Quick fact
A bird's circadian clock acts as a 'seasonal calendar' by measuring day length, enabling it to time breeding with the coming of spring—even in the absence of other environmental cues.
Why this is interesting
Every spring, birds burst into song and build nests—but how do they know when it's time? It's not the warmth or the flowers; it's the length of daylight, and their internal clocks read it like a calendar.