cracking shots !
Are they taken with the tele ? I got a Canon TC-DC58N 1.75x off ebay for £20.00 because the seller said it would only fit a canon camera.
I've found that a tele has a significant effect on depth of field (DOF)for birds at full focal lengths , depending on subject distance.
Theres a useful DOF table here which you can use to calculate the depth of field at a given mangnification for any camera.
http://www.dofmaster.com/dofjs.html
Are you using A aperture setting for your bird shots ? I'd be interested to hear what settings you are using and what your EXIF is for those images.