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Much of what is known about avian navigation results from half a century of displacement experiments with the homing pigeon, the main model in avian navigation. Whether the same processes underpinning navigation in the homing pigeon are also integral to navigation in other species remains an open question. In particular, how Procellariiform seabirds, which routinely travel huge distances over open ocean, might navigate is of interest because of the contrast in sensory environment compared to terrestrial species. In this thesis, I have three aims. First, to investigate whether the mechanisms involved in homing pigeon navigation might also guide Procellariiform seabirds over the ocean. Second, to establish whether GPS-tracked, free-ranging Procellariiform seabirds might be able to offer insights into avian navigational mechanisms. Third, to investigate some of the ecological drivers of long-distance movement facilitated by these navigational mechanisms in Procellariiform seabirds. By combining novel experimental and analytical approaches, I attempt to answer some of these questions. I find that many of the mechanisms though to guide homing pigeons also appear to underpin Procellariiform navigation. In particular, the involvement of information from the time-compensated sun-compass, central to structuring spatial representation in terrestrial species, seems to be very similar to that observed in pigeons. Furthermore, like pigeons, olfaction seems to play a specific role in Procellariiform seabirds’ map sense. However, there are differences too. I make the tentative discovery that, perhaps unlike pigeons, shearwaters might be able to derive information exocentrically about their location at sea in the form of a vector of direction and distance from the home colony, implying a geometric cognitive representation of large-scale environmental gradients. Finally, in terms of ecological drivers of long-distance movement, I find that Manx shearwaters’ migratory phenology is probably constrained by their environment and not by their condition, in-keeping with the idea that long-distance movement comes at a low cost for Procellariiform seabirds.

Humans introduce artificial light at night (ALAN) to the landscape for many reasons - to facilitate commuting to work, to improve their safety and to enhance the nocturnal aesthetics of places. The resulting change in light levels distorts a cue which living organisms use. A cue which, otherwise, has been predictable for billions of years. While some animals adjust to or even take advantage of ALAN, other species respond negatively, with populations suffering due to the presence of artificial light. In particular, burrow-nesting seabirds struggle with light pollution located near to their colony, with thousands of juvenile birds landing in lit-up areas during fledging season – termed ‘grounding’. The aim of this thesis is to investigate the behaviour of seabirds towards light pollution and, ultimately, to understand mechanistically the processes involved in grounding of seabirds. I explore, through observation and experimentation, the behavioural responses of an ALAN-susceptible seabird, the Manx shearwater (Puffinus puffinus) to artificial light. These experiments span the life-history stages of the Manx shearwater, from the orientation of juvenile shearwaters, before and during fledging, to the responses of breeding adults at the colony. I discover that the magnitude, but not direction, of behavioural reactions to artificial light is consistent across these life stages. At each life stage, reactions to ALAN appear to be related to the intensity and wavelength of light, the latter of which implies disruption of the visual system as a root cause of seabird grounding. Finally, in an applied study, I explore the effectiveness that updating old sodium pressure lamps with LEDs has had on shearwater grounding in a coastal town. Overall this thesis highlights the importance of understating the animals’ behaviour towards light pollution at different life stages and locations, contributing to the evidence base for mitigation measures that might be implemented in future.