Do flight-calls of Redwings differ during nocturnal and diurnal migration and daytime stopovers?

Abstract

In the present study, we analyzed 173 spectrograms of acoustic signals of Redwings (Turdus iliacus). These were issued during diurnal and nocturnalmigratory flight and also during feeding, when resting and before take-off at daytime stopovers.During nocturnal and diurnal migration flights and daytime stopovers, Redwings use a single type of signal, a long tsii. It is classified as a species-specific attraction call. In flight Redwings emit shorter calls than during daytime stopovers.We did not find confirmation of the hypothesis that during nocturnalmigration in the absence of visual contact with each other, due to lowlight levels andmuch looser flocks in the course of daytime migration, Redwings emit longer signals with wider frequency spectrum than in the daytime.