Control of the onset of nocturnal migration

• Applicant: Professor Dr. Heiko Schmaljohann
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 258532834

Nocturnal migrants travel without social guidance between the breeding and wintering areas. To arrive at the correct place and time, their innate migration program defines birds` spatiotemporal organisation of migration and their typical reactions to environmental cues. When birds are kept in cages during migration, they show nocturnal activity, called migratory restlessness. The temporal pattern and intensity of migratory restlessness is endogenously controlled. However, changes in photoperiod, temperature and body condition modulate the seasonal pattern. These factors also influence the departure probability of a migrant at a stopover site. Although the circannual and circadian rhythms in migrants and the realised migration behaviour are well studied by cage experiments and tracking of wild birds (radio telemetry, radar, stable isotopes, etc.), we have little information (i) about the exact start of nocturnal migratory restlessness and onset of nocturnal migration within the night, (ii) whether both traits are temporally related, (iii) are strongly endogenous controlled and (iv) which exogenous factors significantly influence the timing of both traits. Knowledge about this is, however, essential for recognizing the mechanisms responsible for the general timing of migration and for the recently observed temporal change in migration. Onset of nocturnal migration defines the potential flight range per night. The seasonal sum of all potential flight ranges per night influences total speed of migration which in turn affects the overall timing of migration. For our understanding of bird migration it is hence essential investigating which endogenous and exogenous factors influence significantly the onset of nocturnal migration. By combining cage experiments to determine the start of nocturnal migratory restlessness and radio telemetry to identify the onset of nocturnal migration for the same individual I will (i) describe the temporal pattern of both traits, (ii) find out whether both traits correlate temporally with each other and identify how (iii) endogenous and (iv) exogenous factors influence the timing of both traits within the night. To this end, Northern Wheatears (Oenanthe oenanthe) will be caught on Helgoland. Due to the small size of the island presence and absence can be precisely determined for radio-tagged birds. On migration the nominate form breeding in Scandinavian and the leucorhoa subspecies breeding on Island, Greenland and in Canada occur regularly on Helgoland. As all Northern Wheatears winter in sub-Sahelian Africa, populations have depending on their breeding areas different total migration distances, different remaining migration distances from Helgoland in spring but not in autumn. This framework allows testing differences in both traits in respect of total migration distance [endogenous factor], remaining migration distance, photoperiod, date of season, temperature, body condition and weather [all exogenous factors].

• DFG Programme: Research Grants