INTRINSIC AND EXTRINSIC DRIVERS OF FORAGING MOVEMENTS IN COLONIAL BIRDS

Foraging is a central trait in species’ life history, being tightly linked to individual fitness and therefore to population processes. To be successful, individuals should forage in a way that minimize energy expenditure and maximize energy intake. However, this balance depends on a mixture of different elements of intrinsic and extrinsic nature, that drive foraging choices of individuals. Intrinsic drivers are elements inextricably linked to individual’s characteristics or qualities that often are a function of age or sex (e.g., dimorphism, social dominance). Extrinsic drivers are elements linked to the surrounding environment, that can be abiotic (e.g., landscape features, weather), or biotic (e.g., heterospecific/conspecific presence, resources distribution). In this thesis I used a combination of bio-logging technologies and statistical modelling techniques to investigate in detail the drivers of foraging movements in different colonial bird species. Specifically, I investigated intrinsic and extrinsic drivers on sea and land (Chapters I and II), the effects of competition (Chapter III), the role of weather (Chapter IV), how food resources can be found in the sea (Chapter V) and its consequences (Chapter VI). My results suggest that a complex interplay of intrinsic and extrinsic drivers shape spatio-temporal foraging decisions in wild bird species, and their combined effect can be sometimes difficult to disentangle. Wind conditions, rainfall, morphological differences linked to sex, inter- and intra-specific competition all affect how individuals optimize their search for food, via the adoption of different behavioural tactics. Moreover, the search for food is particularly challenging in the marine environment, that is extremely dynamic and three-dimensional. Here, individuals could use a combination of static and dynamic features to locate prey aggregations. However, such features also aggregate contaminants such as microplastic, enhancing the risk of ingestion. In conclusion, understanding the connection between individual qualities, foraging movements and external agents is particularly important given the predicted global changes for future years. Ultimately, behavioural flexibility in foraging could be an important trait to successfully cope with such changes and could contribute to increase the resilience of populations over time.