Geomagnetic night vision: a data-driven approach to study geomagnetic navigation in a migratory bird

Geomagnetic navigation during long-distant bird migration is widely debated and it remains unclear which properties of the geomagnetic field birds use and how information might be used. This study is the first use of high-resolution GPS tracking data with co-located and contemporaneous satellite geomagnetic data applied in a step-selection analysis to objectively model geomagnetic navigational strategies in a data-driven approach. We use a day and night-time migrant, the Eurasian Curlew (Numenius arquata) as a model species. Additionally, we test the effect of additional factors (day vs night, spring vs autumn) which have been suggested in the literature or tested indirectly with behavioural experiments. To our knowledge, this study is the first empirical evidence for the effect of night-time and the effect of the angle between the two navigational cues involved (intensity and inclination), on geomagnetic navigation. Our data support previous findings that taxis cue use based on the geomagnetic field intensity showed the best model fit (adj. R² ≈ 0.82 at night) suggesting this as a potential geomagnetic cue use mechanism for animals. The use of a data-driven and step-selection analysis has important implications for future studies of navigational cue use. This can be used for studying interaction effects of different navigation mechanisms, the effect of environmental factors like wind, and the comparison of navigation mechanisms between different species and geographical areas.