550D/t21 - what is happening here?

I thought I was doing everything right when I was shooting these pictures. The bird looks in focus, but when I view it at 100% it is obviously blurry and there is a certain softness to him and not in that tack-sharp-clear focus that I so long to achieve.

I could not increase the shutter speed without it being too dark.

I'm asking for your kind help again.

This visitor comes around every day and my goal is a tack-sharp image of him...please, how do I achieve that with my Canon?

I used the EF-S 55-250mm lens that came with the kit.

Maria