They do have a typical silhouette. Image looks a little soft and there is a lot of jpg compression artifact in the sky - is this a significant crop? A slightly looser crop with the bird a little higher in the frame may be an option. This is another image where it's hard to tell if the bird was coming or going.
I think that this kind of silouette images works fine with an orange BG but not with a blue BG. The first case is a very natural situation (in example a bird against the sunset) but in the case of a blue BG the first impression of the viewer is underexposition and that is not a great thing. I agree about the lack of sharpness. Keep them coming :)