Allen Chartier made observations, recorded data and banded this interesting hybrid warbler on May 14, 2005 at Metro Beach Metropark, Macomb County, Michigan.
Allen writes:
"There seems to be general agreement that one parent is Black-and-white Warbler (Mniotilta varia), while opinions on the other parent are mainly split between Chestnut-sided (Dendroica pensylvanica) and Golden-winged (Vermivora chrysoptera), with "Brewster's" running a distant third. Other possibilities suggested have included Black-throated Green (Dendroica virens) and Black-throated Blue (Dendroica caerulescens), and one suggestion was that this may be a pure Black-and-white Warbler showing some leucism and/or xanthochroism."
Link: More images and information about the warbler.
Hybrid Warbler image used with permission © 2005 Allen Chartier