The number of syllables per phrase in songs of Great Tits Parus major decreases with high levels of anthropogenic noise and at northern latitudes

Abstract

Birds may sing to defend a territory and to attract a mate. However, despite many studies clear conclusions remain on how ecological conditions affect the song, such as physical obstacles that may reduce the sound transmission, and anthropogenic noise that may mask the signal. The social environment of the local populations may also be important, such as breeding density and sex ratio, influencing the number of competing males with which to song match, and the distances to the neighbouring males and to prospecting females. During 2016-19, we counted the number of syllables (notes) per phrase of singing male Great Tits Parus major by visiting seven countries in Europe and one in North Africa. A total of 946 songs were observed by visiting 554 territories. We also recorded study year, anthropogenic noise, calendar date, time of day, type of habitat and vegetation density, latitude, longitude and altitude. The most important explanatory variables were anthropogenic noise and the latitude of the focal site; the number of syllables per phrase decreasing both with increasing anthropogenic noise and with the latitude. The latter result was also supported when analysing sonograms of the species found on the Internet (Xeno-canto), namely fewer syllables per phrase in Norway than in Spain and Portugal. We suggest that repetition of a short phrase is fast interpreted by conspecifics in noisy environments, and that such signals are more readily detected by conspecifics over a wider area where the density of the tits is low.