Back to the original issue with fuzzyness or pixelation. My EXIF viewer says that the ISO was set to 3200 on this shot. Your other bird pictures were shot with ISO around 100. Unfortunately, since I can't see your "original" size image, or at least a 100% crop sample, it's hard to say what exactly is wrong, but I tend to think that it's the noise issue caused by a high ISO selection. You mentioned that you used the "P" mode on the camera. If I recall correctly, in that mode, the camera picks an ISO for you.