OK Mark, you first need to get a reasonable rendering of the sky. This is a big subject and one of the most common second order issues I see on images submitted to our gallery. Very briefly, it usually happens because people try to adjust the colour and lighting of the bird simultaneously with the background. When the sky is the background, problems are bound to arise unless the bird and sky are adjusted separately. In your image the sky has turned out a surreal blue, not even in WA does the sky look like that!. Believe it or not, there are blue sky standards which can get us on the right track although as you know blue sky can have a wide tonal range depending upon time of day, elevation angle and stuff in the atmosphere. A common standard is R = 98, G = 122 and B = 157 which is for mid-day zenith in southern latitudes; generally blue sky is 'paler' in colour than the standard.
To do your canvas extension the easiest way to get a good match is to create a duplicate layer, then go to Image/Resize/Canvas Extension and increase the canvas size vertically by however many pixels you need. This will show as a white space at the top of your frame. Select the blue sky in front of the bird with the rectangular selection tool and then go to Rotate/Flip Selection Vertically. This will flip the selection which can then be moved up the frame after turning on the Move Tool. Once you have a good join between the selection and original image go to Select/Deselect and Flatten the image. You will usually find the join between the selection and the original is not perfect and will need to be touched up with the clone tool. QED.
Cheers, Ian