Abstract
There is a large-scale need to rapidly construct renewable energy infrastructure to mitigate against the climate crisis. This has applied new anthropogenic pressures to many previously less disturbed species, which must legally be considered during the planning and delivery of construction projects. Observing the behavioural responses of individuals to these pressures marks an important cornerstone in identifying the mechanism of response to anthropogenic stressors. However, understanding the consequences of these behavioural responses is needed to accurately quantify any negative impacts. One key area where we lack an understanding of the consequences of anthropogenic activity, is in the environmental impacts of offshore windfarms (OWF). Specifically, it is important to understand the impact of displacement and barrier effects on the behaviour of individuals. Subsequently, linking these behavioural changes to energetic budgets is vital to accurately quantify the consequences of developments on the demographic rates of populations.
Red-throated divers (Gavia stellata, RTDs) have been shown to be a species with one of the highest levels of displacement from OWFs. Therefore, identifying the consequences of displacement for RTDs has become a key research question. Primarily, the effects of disturbance on demographic rates are key to quantifying the stress imposed on a population. Addressing this research question first requires building a more complete understanding of the ecology of RTDs through their annual cycle, as much of their behaviour and ecology is unknown. This is especially true during the non-breeding season, where they are difficult to study, due to their inaccessibility.
To address these questions, I used a combination of biologging, stable isotope analysis and modelling techniques, to build an understanding of RTD behaviour and foraging through the annual cycle. In this thesis, the study populations are comprised of individuals breeding in Scotland, Iceland and Finland, representing three populations on the southern edge of the breeding distribution of this species. I used the newfound ecological understanding of behaviour budgets to explore the energetic costs associated with survival strategies across populations. Finally, synthesising this information, I created an individual based model to simulate the effects of displacement from OWFs on populations and individuals. In many cases, this work provided the first descriptions of key aspects of RTD ecology.
I successfully created the first population-level summaries of diving behaviour for RTDs across the annual cycle and found that RTDs generally dived to shallow depths less than 10 metres. They also showed a mix of benthic and pelagic foraging strategies, with variation both within and between populations. During the non-breeding season, I found that the three separate populations have different behaviour budgets, migration strategies and vulnerability to anthropogenic threats. These behaviour budgets were translated into the first RTD energy budgets, using a novel approach to parametrise an energetics model with allometric scaling equations. The results showed differing costs associated with each of the non-breeding season survival strategies. When simulating the most exposed population to low levels of anthropogenic threats, I found that mortality rates were no higher than those of natural populations. However, when simulating the removal of 45% of foraging habitat, there was a large increase in mortality. Current levels of expected development in most areas of the range of the RTD are unlikely to reach this level.
The work presented in this thesis provides a novel insight into the ecology of RTDs. I also revealed spatial and temporal variation in many survival strategies and quantified the costs of the differing non-breeding season survival strategies. Additionally, these results are contextualised and applied to address a key issue in policy and planning for future offshore wind farm projects.