Species-specific attraction call of the blackbird (Turdus merula) in the periods of seasonal migration and breeding

Abstract

We present the results of the analysis of 346 spectrograms of the species-specific attraction call tsiirr issued during daytime and night migration, at migratory stopovers and during breeding by Blackbirds (Turdus merula). The duration of this type signal varies within the range of 102–359 ms, and its frequency is in the intermediate and high frequency range from 5.1 to 9.9 kHz. In the spectrograms most tsiirr signals have one high-frequency and one lower-frequency modulated band. It is assumed that such a structure of this signal allows the birds to maintain contact at a great distance and to determine each other’s spatial position. Temporary and frequency characteristics of the species-specific attraction calls of Blackbirds during nocturnal and daytime migration did not differ significantly. The species-specific attraction calls during the migration flight had on average a much narrower range of sounding than at stopovers. This difference could have been caused by stronger degradation of the signal structure during propagation in migratory flight than at stopovers. The analysis of the spectrograms of the species-specific attraction calls in two pairs of adult Blackbirds during breeding revealed significant individual variation. Signals of migrating individuals at stopovers were shorter and broader than in adult breeding Blackbirds. Our studies of Blackbird acoustic signals, as well as of signals of two other thrush species, Song Thrushes (T. philomelos) and Redwings (T. iliacus), show that during diurnal and nocturnal migratory flights, they use only one type of signal, the speciesspecific attraction call. This call is also used by the birds for communication during migratory stopovers. No specialized migratory signals are given by thrushes during their seasonal movements.