Song as an indicator of male parental effort in the sedge warbler

Repertoire size has been found to be a sexually selected trait in a number of bird species, although the advantages of mating with a male who possesse s a complex song remain unclear. We studied the potential role of song as a n indicator of male parental effort in the sedge warbler Acrocephalus schoe nobaenus. The male provisioning rate was used as a measure of male parental effort and was found to increase with nest ling age and brood size. When c ontrolling for chick age, brood size and other variables, we found a highly significant positive correlation between a measure of song complexity (rep ertoire size) and male parental effort. Both male parental effort and reper toire size were found to be positively correlated with chick weight when co ntrolling for chick age. We found no correlation between a measure of song output (amount of song flighting) or territory size and parental effort. Re pertoire size is known to be the most important cue in female choice amongs t sedge warblers and we discuss the possible reasons for this. We suggest t hat, in choosing a male with a large repertoire, a female obtains not only indirect benefits but also direct benefits in the form of increased parenta l effort.