Adequate timing of reproduction within the season is crucial for maximising fitness. Although the literature strongly suggest that birds breeding early in the season gain a fitness advantage and that timing of breeding is a flexible decision there are emerging studies showing that breeding early is not always the best solution and that the regulation of timing of breeding is genetically programmed. Thus, early and late nestlings may actually reflect two different adaptive strategies, of which the fitness returns may be context dependent. The research proposal aims 1. To know to which extent the variation in laying date among a kestrel population depends on flexible decisions versus genetic programming, investigating also the degree of genetic differentiation within a Mediterranean population and between different EU populations; 2. To assess the role of assortative mating by time of reproduction in affecting the gene flow among birds living in sympatry; 3. To evaluate the fitness advantage in relation to timing of breeding; 4. To evaluate differential maternal non-genetic resource allocation with laying date variation and 5. To estimate the effects of between years variation of weather conditions on the reproductive success of early and late breeders. I will apply a wide array of techniques, studying mechanisms in an evolutionary framework. The results may challenge the prevalent view of the cause and consequences of timing of breeding, will provide new insight in the evolution of reproductive strategies, and in the genetic structure of raptor populations in different parts of Europe, and may contribute to predict to what extent birds are flexible to react to global warming and how the climate changes could modify the genetic structure of a raptor population.