Well, I met several birders this morning at DeKoevend but did not see the Vireo early (Approx. 0600 - 0630); I went for a run and returned around 0800 and saw/heard him with other birders in trees that line the canal just behind the SSPR Ice Rink along the highline canal where he's been seen before. His song was certainly distinct and he was singing with much gusto although it was hard to pinpoint his location (He didn't seem to want to sit in the same spot very long but you could spot his tail moving during his singing). Perhaps he was sleeping in a bit on what is a beautiful Colorado Sunday morning.
Best Regards, Matt Rodgers