Modelling breeding season foraging and tracking autumn migrations to fill knowledge gaps in gannet ecology relating to impacts of offshore wind farms

Plans for a four-fold increase in the capacity of offshore wind farms (OWFs) in the UK pose a threat to birds that interact with the footprints of such developments. Environmental impact assessments (EIAs), required by law for new renewable developments, typically adopt top-down population projection models to understand how scenarios of collision mortality, displacement and barrier effects impact on a population. Risks outside the breeding season are often only very crudely assessed, and standard techniques used within the breeding season lack the sophistication to capture important processes such as individual specialisation, which may have its own implications for risk. These are the two knowledge gaps that are addressed in this thesis. To investigate risk to different age classes and populations of northern gannets (Morus bassanus) in the southern North Sea, which holds the world’s highest concentration of OWFs, I tracked adult and juvenile gannets from the world’s largest colony (Bass Rock) and reviewed two types of survey data (Chapter 2). I found that juveniles face less risk than adults from OWFs during migration, and an autumn peak of birds in the southern North Sea is likely made up of birds from colonies further north than Bass Rock. To address the need for more sophisticated modelling I used an individual-based model (IBM) approach, which has been used extensively to interpret management scenarios such as the impacts of OWFs. Over the last 20 years individual foraging site fidelity (IFSF) has become a prominent area of research, has been attributed many drivers and consequences, but has yet to be incorporated in IBMs or EIAs. Addressing this required building a model capable of reproducing the movements and behaviour of an individual foraging trip from first principles (Chapter 3), before advancing this model to more behavioural complexity and population-level patterns (Chapter 4). For this purpose I ran simulation experiments to decipher which resource localisation mechanisms, harnessing different levels of public and/or private information, were the best at reproducing empirical patterns of individual foraging site fidelity. The results indicated that memory of several departure angles, learned in previous exploration, plus the ability to react to conspecifics in both an attractive and repulsive manner were key mechanisms required to reproduce IFSF patterns. This finding provides ecological insight into IFSF while also creating a robust behavioural model of foraging gannets that could be applied to understanding the impacts of OWFs in the future. Alongside the potential for more reliable prediction of potential population-level impacts through effects on body condition and breeding success, I argue that this approach could also be useful in forecasting shifting population distributions through its ability to model adaptive populations.