This afternoon I found a Nashville Warbler in the same tree with the continuing Prothonotary Warbler and Northern Parula on the CU Boulder campus. This is the fourth warbler species at this site in two days, although nobody saw the Pine Warbler today to my knowledge.
The warblers have two favorite trees about 50 yards apart. One is a short deciduous tree with yellowish leaves that grows out of a circle cut out of the sidewalk just SW of Regent Hall (near the Lot 309 signs). The other is a yellow-leaved oak a little farther north, along the NE side of Lot 310. The birds started out in the first tree and then moved north into the pines along Lot 310 just now.
The parula has been extremely regular for the past week -- it is almost always in one of those two trees. The Prothonotary is much less regular -- I have only spotted it twice since it arrived. I don't know how long any of these warblers will stay, or what will show up next, but I'm excited to keep checking this spot in the coming days.
Nathan Pieplow
Boulder