Birders,
This afternoon, between 4 and 5 PM while I was exploring the Matthews-Reeser Bird Sanctuary by Lake Estes in Estes Park, I encountered among the decent migrant flocks a Cassin's/Blue-headed-type vireo of whose identity I'm not quite sure. Cassin's is of course more likely on probability, and on top of that I have very limited experience with Blue-headed, but nevertheless, this bird was noticeably quite brightly colored and seemed to have a very contrasting facial pattern. I'd appreciate the opinions of others on this particular bird. Luckily, I managed to photograph the bird before it disappeared, and I've attached a few pictures to this message for the review of others. Here's a link to the eBird report as well, with an additional photo:
http://ebird.org/ebird/view/checklist/S39058674. I have a few additional photos (not as good as the ones linked to here) if anyone else wishes to see them.