Seasonal and Diurnal Patterns of Singing and Song-Flight Activity in Bluethroats (Luscinia Svecica)

Abstract

AnSTRCr.--To assess the functions of male song in Bluethroat (Luscinia svecica svecica), seasonal and diurnal patterns of song and song-flight activity were analyzed by using data on individually marked birds. The seasonal patterns of singing and song-flight activity were found to peak shortly after male arrival and before the onset of egg laying. The diurnal pattern of song production peaked in the early morning (0300-0900), with a less clear increase in song rate around 2200. Male singing activity decreased significantly after clutch initiation. Only unpaired males, or males that failed in their breeding attempt, were heard singing after the egg-laying period. Seasonal and diurnal patterns of song-flight activity were strongly correlated with patterns of singing activity. In addition, male pairing speed was positively correlated with song-flight activity. These results suggest that both song and song flights in Bluethroats serve to attract females. Received 27 April 1993, accepted I July 1993. BLUETHROAT (Luscinia svecica) males are both visually and acoustically conspicuous birds compared to most northern European passer- ines. The song of the Bluethroat is complex (Cramp 1989, Sorjonen 1986) and, in contrast to most other passernes, males often perform con- spicuous song flights (Armstrong and Westfall 1953). Bright coloration and complex acoustical displays of males may have evolved by two dif- ferent means: through either intra- or intersex- ual selection, or both (Searcy and Andersson 1986). In this paper we describe seasonal and di- urnal patterns of song production in the Blue- throat. Our aim was to investigate whether the function of Bluethroat song and song flights was to attract females (result of intersexual se- lection) rather than to defend territory (result of intrasexual selection; Catchpole 1973, 1982, Searcy and Andersson 1986). By using data on temporal variation in singing behavior, we test- ed six predictions where the results of each test