Do flight calls influence orientation of night-migrating birds? [abstract]

Larsen, O N , Andersen, B B , Reichl, T , Kropp, W & Mouritsen, H (2012). Do flight calls influence orientation of night-migrating birds? [abstract]. Bioacoustics, Volume 21 (1): 42 -43

Many migrating passerines emit special calls during nocturnal flight. Several functions of the calls have been suggested. For instance, flight calls have been hypothesized to maintain group cohesion during nocturnal migration and to stimulate migratory restlessness in conspecifics. We wished to test if conspecific flight calls influence the flight direction of a nocturnal migrant, the European Robin Erithacus rubecula. Wild caught birds showing migratory restlessness at night during spring and indicating a stable course were observed through an infrared camera in a sound transparent cage placed in the natural magnetic field inside an echo attenuated room. Two linear arrays of five loudspeakers placed orthogonally about 1.2 meters above the experimental bird could be activated successively to simulate a migrating Robin cruising at a chosen, simulated height (mostly about 40 m above ground), at 10 m/s, and emitting Robin flight calls of 80 dB(A) at 1 m. The simulated flight of a “bell” sound served as a control. The bird was first allowed to settle and express migratory restlessness for at least 30 minutes. Secondly, the flight simulation axis with the largest angle relative to the bird’s migration course was chosen and “flights” of simulated calling conspecifics or of the “bell” sound along this axis continued for 30 minutes. Finally, the bird was observed without sound stimulus. Our pilot results suggest that flight calls of conspecifics influence the mean migratory direction of the experimental birds.