Jim something seems wrong in your shots. Even when using 1.4x TC on 70-200f2.8, you should be getting much sharper shots.
Like woodmeister said, if you redoing your yard to attract birds, do look into sun positions and install bunch of perches near the feeders. You won't need much range if you can shoot from the blind.
I agree, the pictures are not sharp. Cropping and resizing doesn't replace the correct lens. Here is a picture of a robin taken the same day with the Canon 70-200 F2.8. Even with my bad eyes it looks sharper.