Odd Field Sparrow

I have a sparrow that has been driving me nuts on my surveys the last week.  I tried turning it in to every other bird but have finally landed on a field sparrow.  The bird perches on a bush that is not part of my survey property, so I can't just walk out.  Plus, I'm supposed to be monitoring other birds and can only do so much with a non survey species. Yesterday, I tried playing a field sparrow call to get the bird to fly over.  It didn't but a neighboring field sparrow did.  Then, I tried playing a clay-colored sparrow call and the bird flew over--and it doesn't sound like a clay-colored at all.  So, is this a young field sparrow working on his sound?  A really hoarse field sparrow that has been singing like crazy all summer?  Or is a hybrid field sparrow/clay-colored sparrow.  They have been known to occur. Here's a video of a hybrid singing.

I may have to drive down to the survey area on my own time and see if I can get a photo.  The few times the bird has flown by and not hidden itself in foliage, it looked like a field sparrow.  Anyway, here are a few videos of the bird singing: