Thanks everyone for your feedbacks. You are right about the vertical frame. It looks much... much better when I did that.

Srivari; no BG darkening was done. Basically it was at least half f/stop underexposed.

Dr. Kalpamoi Kakati; I couldn't help over exposing the white on wings as there was some direct light fall on that spot.
Regarding the rea half of the bird, as Sabyasachi explained, this is the compromise one needs to make while using the long lenses. Or we need to get the subject in parallel with the sensor.