The high key look works for me here. But maybe tone down the brightness just a bit? And wow, the detail! Looks like you had plenty of pixels on this guy. I can't help but to think that there's too much dead space on the right. I know what you're going for in the comp, but I think it's too much.
The perch does block part of the bird, but it doesn't bother me a bit since you can still see the tail! It looks very natural. Great singing pose too!
I'm liking this alot, Mike. This is how I see them many times, so I really like the perch even if I usually like 'em less busy. Great singing pose too. Good eye in seeing this! Song Sparrows are often overlooked either in nature or on the web - making this image quite under-rated and overlooked IMO.