Carry-Over Effects across Life Stages in Red Kites $\textit{Milvus milvus}$

The study of behavioural differences among individuals, as well as the mechanisms behind it, are increasingly recognized to be crucial for the understanding of demography of animal populations. Throughout an individual’s life stages, external and internal conditions interact, influencing the development of distinct phenotypes. It is the concatenation of these individual-environment interactions that ultimately determines unique fitness outcomes and shapes the population structure, but studies adopting such broad, mechanistic approaches are lacking, probably due to the challenge of collecting detailed longitudinal data. In this thesis, I aimed to build such a mechanistic framework using an extensive large-scale GPS-tracking dataset of red kites (Milvus milvus). Specifically, I first investigated in detail the behavioural dynamics of red kites during development. Then, through the manipulation of food provisioning, I examined how the natal environment can affect the emergence of sociality and further investigated their subsequent survival effects. In Chapter I, I delved into the dynamics of sibling aggression in the nest to better understand how they can shape among individual differences later in life. By adopting a null-model approach, I showed that red kite nestlings strategically adjust how to direct their aggression depending on the daily changes in food provisioning, and that these adjustments associate with a skewed food allocation towards senior siblings when food is scarce, but allow for higher intake of youngest siblings, and thus catch-up growth, when conditions improve. These food-driven aggression patterns can have implications for both the individual physical development and the acquisition of dominant-subordinate personalities. In Chapter II, I investigated how early-life conditions affect the emergence of social phenotypes in the early dispersal phase and tested for their underlying spatial mechanisms. To do so, I combined a supplementary feeding experiment during growth with social network ...