Apart from the composition (the bird rather high in the frame and its tail clipped off), I think the main problem here is the lighting - the top half of the dark bird is in dark shadow set against a dark background, and the natural light was beyond your control.
In post-processing you might try to bring the bird out of the darkness, by increasing the brightness of the background and decreasing its contrast, together with increasing the contrast of the bird and foreground, and some sharpening of the bird, e.g.
Regarding some other points:
The background will be blurred when using a long focal length lens at wide aperture - both parameters reduce the depth of field.
Consider using a higher ISO, e.g. 400 - your Sony should still produce clean images - but you can then use a faster shutter speed, which reduces the chances of motion blur softening the image.
The focus assist lamp is unnecessary in daylight outside, and it might spook a timid creature.
Cheers.
Philip