Endogenous reproductive rhythms in a tropical bird.

Like other tropical birds, African stonechats breeding at the equator reproduce once a year during the main rainy season and subsequently carry out a complete molt. These two activities are controlled by endogenous circannual mechanisms: in stonechats held in constant conditions of photoperiod and temperature, a rhythm of gonadal size and molt persisted for up to 7.5 years, which would be a lifetime for free-living conspecifics. The fact that the period of these rhythms deviated from 12 months demonstrates their true endogenous nature. The results represent the longest circannual reproductive rhythm yet documented and suggest that circannual mechanisms may be of particular importance for reproductive timing in tropical organisms.