In the second photo, it looks like the depth of field is simply too shallow, so the bird's body is in focus, but the eye (which is further away) is not. I will reiterate the other answers and suggest you simply choose a higher aperture number. It's been my experience that kit lenses are usually sharpest around f/8 to f/11. For reasons I don't understand, the depth of field becomes more shallow as the focal length increases (and can become very shallow at long focal lenghts), so you have to stop down the lens further to maintain the required depth of field.
If your camera supports microfocus adjustments, you might try that, as well. However, to my eye, the lens sharpness looks just fine in the center. I suspect you simply need to stop down the lens to a higher f-stop number. Good luck and have fun!