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The distribution and behaviour of the European storm-petrel (Hydrobates pelagicus) at sea
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Date
2025-12-31
Authors
Wilkinson, Darren
Journal Title
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Publisher
University College Cork
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Abstract
Marine ecosystems are increasingly impacted by anthropogenic pressures. Seabirds, as wide-ranging marine predators, are particularly sensitive to these threats, and many populations have declined in recent decades. Understanding the movement ecology and environmental drivers of species distributions is essential for assessing exposure to threats and informing conservation strategies. However, small pelagic seabirds remain among the least studied due to their extensive ranges, high mobility, and often cryptic breeding habits. This is especially true for the European storm-petrel (Hydrobates pelagicus). Although Ireland supports over 20% of the global breeding population, the at-sea distribution, foraging movements, and behaviours of European storm-petrels in the region remain largely unknown. This thesis addresses these knowledge gaps by combining aerial survey data, biologging, and statistical modelling techniques to advance our understanding of the spatial and behavioural ecology of this understudied species.
Chapter 1 provides a broad introduction to seabird ecology and the anthropogenic threats they face at sea. It outlines the use of visual surveys and biologging in species distribution modelling and behavioural analysis, and introduces the European storm-petrel as the focal species.
In Chapter 2, observer-based aerial surveys conducted over four summers in the North-East Atlantic were analysed to estimate storm-petrel abundance and assess environmental drivers of their distribution. This produced the first at-sea population estimate for the entire Irish Exclusive Economic Zone and identified neritic hotspots of abundance, offering valuable insights for marine spatial planning and conservation. Chapter 3 built on this by deploying GPS tags at two breeding colonies, modelling at-sea distributions during the day and night using a Resource Selection Function framework, and comparing results with the aerial survey predictions. The findings confirmed the ecological importance of neritic habitats and demonstrated the value of integrating complementary data sources.
Chapters 4 and 5 advance our understanding of European storm-petrel behavioural ecology using miniaturised GPS devices, some with integrated accelerometers. Chapter 4 presents an approach to classify three distinct at-sea behaviour states (transiting, foraging, and resting) by incorporating accelerometer-informed rest periods into Hidden Markov Models. This method offers deeper insights into the time-activity budgets of European storm-petrels and serves as a practical tool for behavioural analysis in small seabird species. Chapter 5 applies this method to identify nocturnal foraging behaviour, showing through generalised additive models that European storm-petrels exhibit a rare adaptation among seabirds of increased offshore foraging during the darkest nights, likely driven by the availability of vertically migrating prey. This behaviour differs from other nocturnally-active Procellariiformes that typically forage under moonlit conditions. In contrast, nearshore nocturnal foraging was not influenced by lunar light but was instead more closely linked to local productivity.
The European storm-petrel, one of the world’s smallest seabirds and a species for which Ireland is of exceptional global importance, possesses remarkable abilities and adaptations that this thesis helps to reveal. Chapter 6 synthesises these findings, highlighting advancements in our understanding of the species’ spatial and behavioural ecology while also contributing methodological improvements applicable to other small seabird species. Collectively, this work offers the most comprehensive assessment of European storm-petrels in Irish waters to date and provides critical knowledge to inform conservation planning, marine spatial management, and future research on small seabird species.
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Keywords
Seabirds , Foraging behaviour , Species distribution modelling , Aerial survey , GPS tracking
Citation
Wilkinson, D. 2025. The distribution and behaviour of the European storm-petrel (Hydrobates pelagicus) at sea. PhD Thesis, University College Cork.