The study of animal movement has remained of central importance to the study of animal behaviour, as a critical component of how animals survive and reproduce. Through an ever-increasing wealth of telemetry studies, the role of individual decision-making, in response to internal and external cues, has been recognised as important in shaping movement patterns. However, further work is required to better understand the mechanistic drivers and demographic consequences of these decisions, which underpin the long-term stability of populations. As the influence of anthropogenic stressors rapidly increases it becomes critically important to understand the capacity of different species to respond to possible threats.

Here, I study a widespread and generalist seabird, the northern fulmar (Fulmarus glacialis), which has undergone a large population expansion in recent centuries but is currently in decline. Focussing on adult birds breeding at the colony of Eynhallow (Orkney Islands, UK) I build on recent tracking studies and past observational studies of this species, to better understand their individual movement patterns, possible drivers of these and links with breeding success. Fulmars from this colony use a range of movement strategies throughout the annual cycle, visiting the North Sea, the Norwegian Sea, the Mid-Atlantic Ocean and the Barents Sea, resulting in large variation in how far they travel from the colony (< 500 km to > 2000 km).

In Chapter 3, I quantify individual consistency of movement patterns throughout their annual cycle. To separate behaviourally discrete periods throughout the year, I used a combination of daily summaries of location, light level and salt-water immersion, enabling me to quantify inter-annual variation in spatial distributions at individually relevant timescales. I find individual consistency throughout the non-breeding period, including in late winter, despite high levels of population-level consistency at this time and some instances of individual flexibility.

In Chapter 4, I focus in more detail on late winter and pre-breeding, which in fulmars represent an extended period of central place foraging, where they associate with the breeding colony but still spend significant time at sea. There was large variation in trip-taking behaviour in both sexes. Males were more likely to remain resident, but large numbers of both sexes took multiple long foraging trips away from the colony, likely travelling thousands of kilometres more each year than their resident counterparts. I also find that females take longer trips than males and are more likely to revisit familiar areas on pre-laying exodus than males, suggesting biological differences in how fulmars trade off time spent foraging against time at the breeding colony. However, I find no evidence of variation between years, or of carry-over effects linking these behaviours with breeding success.

In Chapter 5, I use high-resolution accelerometry data to describe almost instantaneous flight mechanics and provide insight into how fulmars achieve these highly transitory movements. I find surprising reliance on predominantly flapping flight for a Procellariiform seabird, and evidence that like other seabird species, fulmars moderate their energetic expenditure at different wind speeds, but no clear mechanistic link. Together, these findings suggest that in fulmars the importance of energy gain from dynamic wind features has possibly been over-estimated.

This thesis expands our understanding of the movements of fulmars throughout their annual cycle, at broad and fine spatial and temporal scales. Making use of long-term data, I demonstrate how additional insight can be gained by using individually specific pattern recognition techniques, to augment the interpretation of low-resolution data. Additionally, I demonstrate the value of state-of-the-art high resolution data loggers, to mechanistically understand how broad-scale movements are achieved.