Worm-eating Warbler extended (flight) song

A number of warblers have a so-called flight song, most often given at twilight, and not necessarily in flight, which is more extended than the regular song eg Ovenbird, Louisiana Waterthrush and Common Yellowthroat. Earlier this week I was observing a family of Worm-eating Warblers and picked up the extended version of their song. The birds were foraging and uttering various notes including the chip alarm and flight calls (high, often doubled or tripled buzzes). Also heard are twitters, and the song itself, which in the most extended version is a t-t-t-ch-ch-ch--wee-wee-tu-tu-tu- trill-wee-wee-tu-tu-tu-ch-ch-ch-wee-wee. It did not seem to be given in flight, but more by a bird that was agitated/excitable. Given that songs are learned, presumably this song is given more commonly than supposed, as the young males must need to learn this song along with the regular one that is sung. Alternatively, the song may be improvised. Of interest, it appears that those warblers that have a well-described flight song sing only one version of the regular song. Perhaps the flight song is one of aggression, equivalent to an unaccented song?