Beautiful bird and razor sharp.
Was this a crop, and if so was there space above the bird that might have allowed you to place the warbler lower in the frame? Not sure if that would improve the composition but there seems to be a lot of negative space below the subject that to my eyes doesn't help the overall look. Just my initial thought and perhaps this is a frame filling image with no room to experiment with alternate compositions but if possible I might have placed the bird lower in the frame with more open space above and perhaps to the right of the main subject.
It really is a nice image and the main subject is great in terms of color, contrast, sharpness and the like but to my eyes the composition feels a bit cramped and maybe off a bit.