Here is a summary of the comments I received on the Philadelphia Vireo record, 2011-38.  I've added a brief bio based on what I knew or could find about each commenter's bird ID credentials.  All comments were sent to my personal email, not to the FRID listserv.  

Comments:

Joseph Morlan (California, author of several books and journal articles on bird ID):
"It's not acceptable as a Philadelphia Vireo for a bunch of reasons.  But it looks very promising to me as a YELLOW-GREEN VIREO."

Cliff Weisse (Idaho Bird Records Committee, eBird reviewer):
"Since much of the discussion on ID Frontiers isn't on the list I'd appreciate hearing what you learn about the vireo.  I looked at the photos when they were originally posted and couldn't decide what it was either."

Oscar Johnson (Hawaii eBird reviewer, Montana State U. ornithologist) and Jim Tietz (indirectly; Biologist, Point Reyes Bird Observatory):
"I saw the photos of that vireo from Utah.  I think you might be right in thinking hybrid on that one.  I showed the photos to Jim Tietz who saw the Farrallones bird [the PHVI x REVI hybrid I linked to in my first round comments], and his comment was that the Utah bird was quite different structurally."

Richard Crossley (author of the Crossley ID Guide [forwarded via Tony Leukering]): 
"Tough.  I would like to have seen this in the field.  >From these 2 images it certainly has a Warbling Vireo feel in bill, overall shape and fairly long tail.  As you know, this is a very variable species, some being quite extensively yellow and can show dark lateral crown stripes.  So what says this is definitely not an extremely bright and strongly marked Warbling Vireo?  From this photo I am not sure there is anything.  People may argue it is too yellow but I don't think I would agree.  Having said that, in the field this may have looked like a totally different beast.  If it is a hybrid, why not Warbling x Philly?  The Red-eye x Philly does not seem an obvious fit to my eyes, particularly in structure.
"In short my answer is, I don't know.  As a records committee member I would not accept this as a Philly Vireo based on just these 2 images.  I would also not try to guess what it is either.  Wish I could help more."


Good luck wrestling with this one!
-Ryan
 
Ryan P. O'Donnell
Ph.D. candidate
Department of Wildland Resources and the Ecology Center
Utah State University
5230 Old Main Hill
Logan, UT 84322-5230