AbstractWild zebra finches,Taeniopygia guttata, sing frequently throughout the year but the function of undirected song, the most prevalent type, is unknown. Paired males commonly sang undirected song in feeding flocks where it occurred more frequently in the non‐breeding season than in the breeding season. Song rate varied greatly among males. The context of the singer and the absence of any overt responses from flock members excludes direct aggressive and mate‐attracting functions. Performance of undirected song may have energetic costs and predatory risks. The finding that singers are active individuals with ‘spare time’, that are neither hungry, nor tired, nor sexually motivated, suggests that singers are advertising their ‘quality’ as potential mates and/or participants for extra‐pair copulations. When the female partner in non‐breeding pairs was experimentally removed, the rate of undirected song of the ‘widower’ increased significantly. Males quickly re‐paired. This experiment supports the hypothesis that singing in the flock has a
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