Mechanisms and fitness consequences of laying decisions in a migratory raptor

Seasonal decline in breeding performance is a commonly observed pattern in birds, but disentangling the contributions of environmental conditions (“timing” hypothesis) and individual quality (“quality” hypothesis) to such a pattern is challenging. Moreover, despite the strong selection for early breeding, the individual optimization model predicts that each individual has an optimal breeding window. We investigated the causes and consequences of laying decisions in the lesser kestrel (Falco naumanni) by combining a long-term dataset on reproductive traits with information on food availability. A marked seasonal decline was found in breeding success, mostly mediated by a decline in clutch size. The “timing” hypothesis, supported by the decline in consumption of mole crickets, key prey for prelaying females, seems to explain the seasonal trend in clutch size, as this pattern was recorded in both higher (adults) and lower (yearlings) quality individuals. Contrarily, the higher proportion o...