Circannual rhythm of a male African stonechat. This bird was kept under continuous 12 hour daylength for over 10 years, and its reproductive and moult cycles were recorded. Each line of this plot represents a new year. The bird underwent regular cycles, but both activities occurred successively earlier each year. This is clear indication of a freerunning circannual cycle; from Gwinner 2003, https://www.sciencedirect.com/science/article/abs/pii/S095943880300165X