The lesser whitethroat is a migratory species commonly breeding in Denmark over a wide range of closed habitats. It arrives in Denmark in late April and is either single- or double-brooded. During 1994 and 1995, six and eleven pairs respectively were followed throughout the breeding cycle. Eleven of the males were individually colour-ringed. The song of the males was recorded for a ten minute period each day. All nests were found before the clutch was completed, so the day of the first egg could be determined. I present results showing that song activity is high from arrival until 3-5 days before the first egg, when there is an abrupt decline in activity. This corresponds to the time when the female becomes fertile. A common hypothesis for song function is that it serves as mate guarding. This cannot be the case for the lesser whitethroat. Instead, I suggest that the closed habitat makes it advantageous for the males of this species to stop singing and guard the female without drawing the attention of other males. Furthermore, results from an analysis of function of the two different song types (twitter and trill) in lesser whitethroat throughout the season are presented.
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