Sensory Processes Around Ocean Fronts: Insights from Seabird Bio-Logging in Three Dimensions

Fronts attract seabirds, but the sensory mechanisms that underpin this process are poorly understood. Visual cues indicating the presence of prey-rich frontal areas include water colour and texture, but more conspicuously, scavengers and other predators. Olfactory cues include dimethyl sulphide, which Procellariiform seabirds are known to use to locate food and navigate during non-foraging flights. The northern gannet Morus bassanus is a large piscivorous seabird that associates with other marine predators, and is more likely to perform area restricted search behaviour around fronts, but only persistent and predictable fronts. Gannets visually detect underwater prey from the air before plunge-diving, they lack external nostrils and have smaller olfactory bulbs than procellariiformes, suggesting that vision is key. However, we do not know if they locate prey at larger spatial scales using vision alone or if olfaction plays a part. As olfactory cues are stronger close to the surface and visual cues are stronger at height, we investigate the relative contributions of vision and olfaction using fine-scale 3D movement data (GPS, altitude, acceleration, dive depth). We analyse altitudinal adjustments in the lead-up to foraging behaviour and in the presence of strong and persistent frontal zones. Accelerometers detect fine scale movements that are not detected in GPS tracks alone, allowing us to look for typical crosswind and odour plume following flights, which have not been previously detected in gannets. Ocean fronts are identified using composite mapping that combines remotely-sensed sea surface temperature over several days, reducing cloud-related data loss and the impact of strong but short-lived fronts. The combination of bio-logging and remote sensing has revolutionised our understanding of how seabirds interact with their environment, and reconstructing 3D movement is an informative new way to study species that use aquatic or aerial habitats.