I have to say the heavy crop is showing. Details are lacking, and the noise is accentuated by said crop and over-sharpening. As is it is cropped rather tight, I'd suggest adding some back. Also best to avoid body parts being clipped by branches and frame's edge, and the OOF one running along the back and head is unfortunate. On the plus side you did get a nice look-back pose from this fella. You'll have a tough time photographing birds with 100mm. If this is the longest lens you have I'd suggest starting off with tamer larger birds...perhaps habituated ducks, geese, or gulls from a local park (or someting similar).