The mechanism and development of avian navigation
Keywords: navigation
seabird
development
magnetoreception
songbird
birds
inheritance
migration

The mechanisms by animals navigate are central not only when considering how animals interact with the environment, but also how the environment shapes and guides animal evolution. Some of the most remarkable feats of navigation in nature are undertaken by birds, with long-distance, transcontinental and trans-oceanic migrations found throughout the avian clade. However, despite being of fundamental interest, the development of avian navigation remains imperfectly understood. In this thesis I seek to use historic ringing data alongside modern biologging technology to investigate the mechanism and ontogeny of long-distance movement, using both correlative and experimental analyses and drawing on examples from across the avian phylogenetic tree. First, I consider the mechanisms of outbound migratory inheritance, finding that Manx shearwaters (Puffinus puffinus) are unlikely to follow their parents on first migration. I suggest that this implies that shearwaters are likely to inherit migratory information genetically, and speculate that genetically inherited information could also underpin return migration even in animals where outbound and return migratory routes differ. Second, I find that great frigatebirds (Fregata minor) exhibit a rapidly learnt ability to compensate for wind drift, and I suggest that such an ability could be predicated upon either visual information or sensory gradients cues. I propose that a learnt ability to compensate for drift may arise early in development, and could be of use to migratory taxa more generally. Third, I find evidence for the use of magnetic spatial information in both a songbird (the Eurasian reed warbler; Acrocephalus scirpaceus) and a seabird (the Manx shearwater) when relocating the natal/breeding site (‘philopatry’) following migration. Specifically, I find that magnetic inclination, learnt prior to departure, might be used as a uni-coordinate ‘stop-sign’ on a return migratory vector to guide return migration. Further, by mathematically modeling year-on-year variation in the Earth’s magnetic field, I suggest that the use of uni-coordinate magnetic information might be less affected by magnetic secular variation than a bi-coordinate magnetic ‘map’, and hence might be a more evolutionarily advantageous solution to the problem of natal homing. Finally, using a twilight cue manipulation paradigm, I find evidence for the use of a magnetic compass by a pelagic seabird, the Manx shearwater. I find that rotations in the Earth’s magnetic field at dusk predict deflections from the beeline during homewards orientation, with the magnitude of these deflections predicted by discrepancies between the inclination of the artificially applied magnetic field and the inclination of the normal magnetic field. I suggest that this inclination sensitivity is consistent with the use of an inclination compass, as seen in songbirds. Overall, I discuss the evolutionary and environmental determinants of navigational mechanism, and propose future experiments and analyses that could elucidate the development and mechanism of long-distance navigation across avian taxa.