Bestand und Verpaarungsstatus von Nachtigallen 'Luscinia megarhynchos' im elsässischen Rheintal bei Basel

Untersuchungsgebiet Petite Camargue Alsacienne In 2003, we censused singing Rufous Nightingales in a study area of 17.9 km2 between Saint-Louis and Kembs-Loechlé (France). Three surveys were made during the day and one at night. We counted 194 singing males, 83 of which were heard only during the day, 38 only at night, and 73 both at day and night. Since male Nightingales usually stop singing at night after pairing, we suggest that the 111 nocturnal singers were mostly unpaired males, while the minimum number of paired males would be 83. However, Nightingales were less easily heard during the day than at night. Based on the results from an intensively examined part of the study area (the Petite Camargue Alsacienne), we assume that the actual number of paired males was higher than 83 and that the population size was up to 240 males, about half of them being unpaired. We suggest that the high proportion of unpaired males reflects a strongly male-biased adult sex ratio and discuss implications for sexual selection and the interpretation of bird census data.