Jack Swelstad took pictures of this warbler he found in his yard in Brown County, Wisconsin. It appears to be a Sutton's Warbler (Yellow-throated x Northern Parula hybrid). We published a note about this in the Wisconsin state bird journal Passenger Pigeon.
Anich, N. M., J. A. Swelstad, and B. Pierce. 2012. The First Report of Sutton's Warbler
(Northern Parula × Yellow-throated Warbler) in Wisconsin. Passenger Pigeon 74:149–155.