Also, about the ratio. I think it would be good to try a different ratio but not with this picture. It's fine as is. Try a different POV.
Further about the bird and the composition. I think it's really key here. Your eye is drawn to the right side of the picture. There is drama with the light there. Darker trees against the picture frame. A lot of dark weight in the right bottom corner. More mountain on the right and contrast where it's being lit. The left side has less interest. The drama with the dark cut off bird against the sky creates balance, drawing your eye away from the lighting on the right.
Also notice the rockier top of the mountain in the middle of the picture framed with two trees on either side almost thirds through the picture. Then the rhythm of two more smaller trees. There is rhythm in the ones near the edges of the picture as well but light on left, dark on right. The little wisp of cloud on the left near the bird. Honestly, this is a great picture as is. There are lots of elements that make it work.