The function of migratory bird calls: do they influence orientation and navigation? Thomas Reichl1, Bent Bach Andersen2, Ole Naesbye Larsen2, Henrik Mouritsen1 1Institute of Biology, University of Oldenburg, Oldenburg, D-26111 Oldenburg, Germany 2Institute of Biology, University of Southern Denmark, Odense, DK-5230 Odense M, Denmark Many migrating passerines emit special calls during nocturnal flight, the so-called flight calls. Several functions of the calls have been suggested but largely remain speculative. Flight calls have been hypothesized to maintain groups 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), i.e. if flight calls help migrants keeping course. Wild caught birds showing migratory restlessness and indicating a stable and constant course were observed successively through an infrared camera in a circular sound transparent cage placed in the natural magnetic field inside an echo attenuated room at night during spring. 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 E-W, W-E, S-N or N-S at a chosen height (mostly about 40 m), at 10 m/s and emitting Robin flight calls of 80 dB(A) at 1 m. The simulated flight of a "ding" sound served as a control. During an experiment the bird was first allowed to settle and express migratory restlessness for at least 30 minutes. Secondly, the flight simulation axis (e.g. E-W or N-S) with the largest angle relative to the bird's migration course was chosen and "flights" of simulated calling conspecifics or the "ding" sound along this axis continued for 30-60 minutes. Thirdly, the stimulus was switched off and the bird was observed for 30-60 minutes until, fourthly, "flights" of the opposite sound was performed for 30-60 minutes along the same axis. Finally, the bird was observed without sound stimulus. Our results indicate that flight calls of conspecifics influence the mean migratory direction of the experimental birds.
Flight calls; orientation; navigation; magnetic compass; Erithacus rubecula
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International Conference of Comparative Physiology and Biochemistry "Molecules to Migration", 2008