Black-headed Gull in flight

I have been working on my unprocessed images this week. I have almost discarded this photo because the gull was in the left bottom corner, but liked blurred wings and their position so I decided to work on it in PS and clone the sky to the left of the gull (about 1/4 of the width). I was suprised with the result. The golden-blue background to the right of the gull is untouched - it is probably out-of focus clouds. It was early morning golden light.

Is cloning of the sky a common practice?

The technicals:
EOS 10D + 400/5.6L handheld, ISO 200, 1/400s f5.6, the gull on original image is about 50% of the width of the frame, so it is almost equivalent to the original uncropped image.

Fero