|The Petite Camargue Alsacienne is situated in the Upper Rhine Valley, which is home of a dense population of nightingales (Luscinia megarhynchos). In 2003, we counted 194 singing males in a study area of about 18 square kilometres (see illustration below). Since 1997, we capture and ring nightingales in a study area of one square kilometre, in up to 28 territories per year. Another important basis for our studies are regular nocturnal rounds of inspection at the study site. Since only unpaired males sing regularly at night, we can determine the mating status of males by observing who sings at night and who sings only during the day. Once they are paired, male nightingales usually stop singing at night (Amrhein et a. 2002, 2004a). This suggests that the famous nocturnal song plays a role in mate attraction. In experiments using song playback before the arrival of females, we found that prospective mated males overlap more songs of the playback, i.e. seem to sing more aggressive, than do males that remain unpaired throughout the breeding cycle (Kunc et al. 2006). Females could thus gain information on the quality of males by listening to the nocturnal singing.
As in many other songbird species, male nightingales sing most during the hour before sunrise. During this dawn chorus, not only unpaired males but also paired males sing throughout the breeding season (Amrhein et al. 2004a; Kunc et al. 2005a). Dawn singing may thus be important to defend the territory against other males. This might be crucial especially if some unpaired males leave their territories in the course of the breeding cycle to become so-called floaters, and to prospect other territories before sunrise. Each year, up to 49% of the males remain unpaired (Amrhein 2004), and non-territorial males that were followed using radio-telemetry truly visited up to five occupied territories during the hour before sunrise (Amrhein et al. 2004b).
By means of radio-telemetry we could also show that territorial male nightingales intrude into the territory of their neighbour after that neighbour was challenged by a singing intruder (simulated by playback; Naguib et al. 2004). Male nightingales thus respond to territorial problems of their neighbours and can be considered members of an interactive communication network. Currently, we make paternity analyses with blood probes that we collected since 1998. First results suggest that the rate of extra-pair fertilization is not particularly high (about 7.5% of offspring; Amrhein 2004).
Study area (light grey) with the Petite Camargue Alsacienne (PCA). Dots are 194 singing nightingales and 8 additional territories in the Petite Camargue that were not monitored during the four censuses. From Amrhein & Zwygart 2004.