On real close examination after you bringing it up, I too can see a very slight halo around the bird, though I did minimal sharpening using lab mode. The clear blue sky brings it out,
My eyes can see maybe a slight smudge in right top corner where I removed small part of feeder using content aware & didn't do any cleanup.
Gus, he's a cutie! You've already mentioned the slight halo - you might try cleaning that up with a soft brush edged right up against where the two colors meet.
Also, his neck seems a bit darker than normal - can you get a bit more detail out of it?