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It has been widely acknowledged that a global change in energy production, from fossil fuels to renewable sources, is required in order to reduce carbon dioxide outputs and help mitigate anthropogenic climate change. The UK is recognised as having one of the largest practical marine energy resources in Europe, including ‘wet renewables’ energy sources; tidal-stream and wave energy. Scotland, as well as having some of the best marine energy resources, also holds internationally important numbers of breeding seabirds. Both wave energy and tidal stream devices have the potential to place a new anthropogenic pressure on already declining seabird populations. Wet renewables are predicted to impact seabird populations through collision, disturbance, habitat loss and changes to food availability. However, few devices have been deployed to enable monitoring of impacts and there have been few studies of the ecological implications and magnitude of any impacts to these populations. The aim of this thesis is to address key knowledge gaps relating to our understanding of seabird ecology in high-energy marine environments, specifically exploring spatial, temporal and habitat drivers for their use of these areas. This is to help expand the scientific basis used to assess the impacts of marine renewable energy devices on marine birds. This thesis also aims to increase our understanding of bird survey requirements for wet renewable energy schemes to help develop methods for environmental impact assessment. Chapters 2, 3 and 4 demonstrate that marine birds show differing spatial and temporal patterns of abundance and behaviour within high-energy marine environments. By using shore-based vantage point methods in three high-energy areas in the Northern Isles, I explore some variations in vantage point methods. Chapter 5 provides the most extensive and up-to-date review of diving and foraging behaviour for UK marine bird species. I identify knowledge gaps including the species and parameters for which there are a paucity of studies. I demonstrate a more robust approach to data collection in these high-energy tidal stream, which can shed insight on how they are being used by marine birds, while the diving and foraging behaviour synthesis provided many of the values that are required to undertake underwater collision risk modeling. It is hoped that developers can adopt the approaches identified here, which will improve the accuracy of their assessments and improve monitoring of any potential impacts.

Recent bio-logging technology and associated techniques have uncovered the distribution, behaviour, and phenology of marine predators at remote locations, providing us with insights of not only scientific merit, but also in terms of conservation and management. This thesis explores the at-sea behaviour of marine birds using field studies and ethoinformatic approaches by using multiple data loggers, focusing on four species of free-ranging seabirds breeding in the UK. Key findings and conclusions are: Extending travel distance in central place foragers in the wild is associated with higher prey quality as estimated by an indirect method based on dive profiles. This result is consistent with a prediction of optimal foraging theory, but my results show empirically that seabirds are able to increase reward with distance at the extended scale of the marine environment. Razorbills Alca torda are capable of adjusting their foraging behaviour in response to proximate environmental conditions. The potential mechanisms underlying this adaptive behaviour are independent of breeding stage, but the magnitude of flight orientation is scale-dependent. These results suggest that Razorbills are capable of optimising their foraging adaptively, possibly reading cues from the environment or conspecifics. Diving behaviour in sympatric Atlantic Puffins Fratercula arctica and Razorbills is very similar, in contrast to the predictions of the competitive exclusion principle. They are likely to be near carrying capacity for the location and this may explain why Skomer’s Razorbill population is declining while its puffin population is stable. Differences in foraging trip duration of chick-rearing Manx Shearwaters Puffinus puffinus reflect differences in resource allocation between provisioning offspring and self-feeding. I developed a model based on patch quality and travel time to show that birds should use bimodal foraging trip durations to optimise feeding rates for their offspring. Individual reproductive performance in Manx Shearwaters can be predicted from previous breeding phenology and is linked to differences in overwintering behaviour patterns. This carry-over effect reveals the existence of a trade-off between current parental investment and future reproductive performance.