Understanding the responses of coastal seabirds to fine-scale environmental variation

Abstract

Marine environments are highly heterogeneous across a range of spatiotemporal scales, forming a dynamic patchwork of habitats and variable environmental conditions in which seabirds must forage, grow, reproduce and survive. Numerous studies investigating the responses of seabirds to environmental variability focus on regional (>100km) and long-term (seasons-years, interannual) processes to explore the influence of environmental variability on aspects of seabird ecology, including behaviour. However, the underlying mechanisms linking seabirds with their environment are likely to occur at the fine spatial (local: <10km) and temporal (acute: minutes-hours) scales at which seabirds encounter and interact with their immediate environment. Therefore, without understanding how seabirds respond to environmental variation at fine spatiotemporal scales, predicting the impacts of future climate change lacks appropriate resolution. Furthermore, as environmental conditions typically differ within regions, neighbouring populations may respond differently to climate change, making extrapolating findings across populations inappropriate. This is likely to be particularly pertinent for coastal seabird species which tend to have short-home ranges and a reliance on continued access to localised prey resources within near-shore environments. Inhabiting coastal environments year-round, the European shag Gulosus aristotelis and great cormorant Phalacrocorax carbo are particularly susceptible to the impacts of environmental variability and adverse weather conditions due to their partially wettable plumage, high energetic flight costs and their requirement to return to land between periods of foraging. Given the vulnerability of these species to environmental extremes, and in light of increasing environmental variability due to climate change, there is a pressing need to expand our understanding of how seabird species and populations respond to environmental variability at fine spatiotemporal scales.

This thesis investigates the behavioural responses of two coastal seabird species, the European shag Gulosus aristotelis and great cormorant Phalacrocorax carbo (hereafter collectively ‘Cormorant spp.’), to fine-scale environmental variability (local: <10km, acute: minutes-hours), specifically the influence of predictable and continuous tidal cycles, and unpredictable and intermittent weather conditions on foraging activities. Focussing on the previously understudied populations of shag and cormorant breeding on Puffin Island and inhabiting the highly dynamic Conwy Bay and the Menai Strait, north Wales (UK), I apply a range of technology-based monitoring methods to explore population- and individual-level behaviours relative to variable environmental conditions. Firstly, I evaluate the application of remote camera technologies and automated image detection methods to monitor offshore daytime roosts, providing guidelines and recommendations for the application of such methods within future seabird research. Secondly, I investigate population-level responses to weather conditions during the non-breeding season using timelapse cameras and manual image analysis. I identify opposing patterns of roost use across sites and propose that habitat-switching could be a probable or likely mechanism by which Cormorant spp. may extend their use of a system across a range of environmental conditions. Thirdly, using biologgers I explore how individual-level foraging activity and choice of foraging habitat type by breeding shag responds to variable dynamic environmental conditions (weather and tides). I strengthen existing evidence that shag predominantly forage in shallow, flat and sandy habitat types, and highlight diurnal patterns of foraging presence within this habitat type. I also show that predictable physical processes (ebb-flood tidal cycle) may be more influential than weather conditions in determining where shags forage during the breeding season.

Collectively, the work presented in this thesis represents the most comprehensive study into the behaviours of European shag and great cormorant in the Irish Sea and provides novel insights into the behaviour of these species. By demonstrating the advantages and challenges of applying technology-based approaches to seabird monitoring, this thesis contributes to furthering the development and application of wildlife monitoring technologies. Overall, the findings presented in this thesis advance our understanding of how coastal seabird populations respond to environmental variability. Furthermore, this thesis demonstrates the importance of continuing to expand our knowledge and understanding of populations across a broad geographical range.

Date of Award	18 Aug 2026
Original language	English
Awarding Institution	Bangor University
Sponsors	Envision DTP
Supervisor	James Waggitt (Supervisor) & Jonathan A. Green (Supervisor)