Correction: It turns out I did not actually see a Philadelphia Vireo. It was a more-yellow-than-usual Warbling Vireo. Oops. But the next day I went back to Arrowhead Prairie with hopes of seeing the newly reported Sedge Wren. I got it, plus another life bird in Bobolink, for year birds #140 and #139 respectively.
This male Bobolink is molting into his basic plumage for the fall, which is why he looks so weird. I was unable to get a photo of the Sedge Wrens and actually only saw one of them for a split second as it flew up above the grass before diving back down into cover. But two were calling back and forth the whole time, making the ID fairly straightforward.