I'm not sure if you have the IS version of that lens or not, but either way, that lens is not known for producing sharp pictures, especially at the 300mm range.
The other problem with the lens, is that it really doesn't have the range for birds. Sometimes teleconverters can be added to increase the range of a lens, but because this one is already too soft at the long end, adding a teleconverter is really not an option.
The files you posted are pretty small for pictures, so it might be possible to shoot at a higher quality setting and then crop the pictures, but the pictures you referecenced are too soft to crop. I tried it on the bluebird pic, but the results weren't good.
Sorry to be so blunt Surfcaster, but there really isn't any nice way to put this. About your only option with that lens is to get closer where you don't have to use the 300mm range, but that's usually pretty difficult when your subjects are birds.
One thing you might want to do, is take a look at bird photos taken by others. Normally with birds (and other wildlife), you want to fill most of the frame with the bird. Here's a link to some of the best bird photo's I've seen: