Proc. R. Soc. B doi:10.1098/rspb.2008.1726 (2009)

Male nightingales that sing during the night are serenading females, whereas those that sing at dawn are letting other males know that the territory is occupied, report Tobias Roth of the University of Basel in Switzerland and his co-workers.

The researchers caught ten female nightingales (Luscinia megarhynchos) and moved them 70 km to a site in the Rhine Valley in France where the team has studied nightingales since 1994. Radio transmitters glued on the backs of the incomers revealed that unpaired females fly around at night visiting several males, at a time when bachelor males are singing more frequently than paired males. All males sing vociferously during the dawn chorus, however.