We examined different song parameters leading to a complex song configurati
on, and song output (production), and their relation in male Moustached War
blers and discuss them with reference to female choice. With more than 120
different syllables per two minutes of song, male Moustached Warblers can b
e regarded as one of the most complex singers within the genus Acrocephalus
. We found significant differences between males for almost all song parame
ters investigated (repertoire size, switching and repetition rate, song spe
ed and strophe length) but not for time spent singing per 20 minutes. This
individual variation probably is an important cue for female mate choice. M
ale Moustached Warblers achieve song complexity mainly via frequent syllabl
e switching. Song complexity seems to be consistent throughout the song and
our results suggest that females could assess the overall song complexity
of a singer by examining even very short song bouts. Furthermore, a high pr
oportion of motifs - clusters of syllables with the same sequence - occurs
within the song of each male which would also Facilitate assessment of song
complexity by females. However, repertoire size and strophe length were po
sitively related, thus it remains to be investigated which song feature, if
any, females actually use.