Mechanisms of long-distance navigation and the time-compensated sun compass in wild shearwaters

Thesis

Decades of research have shown that birds attend to the motions of our planet and distant stars to navigate across the earth. Yet how such cues contribute to guiding their natural movements remains largely a mystery because the animal navigation literature has relied heavily on captive or incarcerated birds, motivated to orient either by displacement or migratory restlessness. In this thesis, I utilise the growing body of tracking data from the free-ranging movements of wild shearwaters to investigate the sensory and cognitive mechanisms of a wild avian navigator. I achieve this by leveraging errors inherent in the constraints of putative navigational mechanisms or induced by sensory manipulation. First, I exploit the highly conserved mechanisms of circadian entrainment to predict that Manx shearwaters (Puffinus puffinus) might experience jet-lag-like time shifts during rapid longitudinal flights, causing errors in use of a time-compensated sun compass. These errors reveal that shearwaters use the sun compass to home after their natural foraging trips, apparently as the primary compass cue when out of sight of land, and integrate information from land when coast-following, perhaps by visual pilotage. Further, capitalising on this interaction between use of the sun compass and coast-following, which can be detected without a priori knowledge of the shearwater’s goal, I show that shearwaters use the sun compass while commuting towards foraging grounds. I build on these findings using an artificially induced clock-shift, and show that the timing of shearwaters’ foraging movements is influenced by their endogenous circadian clocks. I next find that shearwaters do not appear to rely on geomagnetic cues to calibrate their time-compensated sun compass, nor indeed for any part of their homing navigation. The last empirical chapter of this thesis investigates the spatial representations which facilitate distance estimation in the migration of Balearic shearwaters (Puffinus mauretanicus), and the contribution of this spatial cognition to individual migratory flexibility and population range shifts under climate change. Finally, I consider surprising parallels to the navigation of homing pigeons (Columba livia) and the implications for the evolution of navigational mechanisms; the value of data on the free-ranging movements of wild birds for investigating navigation, especially beyond homing and migration; and the potential this provides for studying the behavioural ecology of navigational and chronobiological mechanisms.

Authors: Lewin, P

• DOI: 10.5287/ora-44daabppk
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: movement ecology; spatial cognition; sun compass; animal navigation
• Subjects: Bird navigation