The Golden-winged song of the bird that you heard (but did not see) may have come from a Brewster's Warbler (hybrid between Blue-winged and Golden-winged). Brewster's have been known to sing Golden-winged songs. See http://elibrary.unm.edu/sora/Auk/v045n04/p0511-p0511.pdf
 
We had a Brewster's Warbler at Weston Bend S.P. in 2000 and 2001. After that, a back-cross individual (Brewster's x Blue-winged?) was noted there. Perhaps even more remote back crosses, which look entirely like Blue-winged's, may still give the Golden-winged Song from time to time.
 
After finding the Brewster's at Weston Bend, I often wondered what it was doing there. Presumably, it was hatched in an area of sympatry (range overlap) between Blue-winged and Golden-winged in Wisconsin or some other place hundreds of miles to the north, then lingered on migration to mate with Blue-wingeds at Weston Bend.
 
 
Bob Fisher
Independence, Missouri
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