Photoperiodic Control of Reproduction and Molt in the Kestrel, Falco tinnunculus

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Abstract
An adaptive decline in average clutch size with progressive date of laying is char acteristic of most bird species with a single clutch of variable size per year. The effect of photoperiod on timing of laying, clutch size, and subsequent molt was investigated in kestrel pairs breeding and raising their young in captivity. In natural daylight (nLD), clutch size, under ad libitum feeding, showed the same decline with date as in nature. Birds breeding later also started molt later and molted faster (more feathers simultaneously), so that all birds completed molt more or less at the same time.