Very good game, lovely artstyle and a cute idea. I can't relax to it though because the controls for turning are far from precise. I can't feel immersion when on a light touch of the key the camera turns by such a huge angle compared to how I actually would like it to turn. The best examples for better controls that I can think of are "Fly like a bird" games, at least the 3rd which I played, or even the old "I of the Dragon". Basically the camera shouldn't (to me!) go so far sideways when you turn and the turning should be much slower, with a slight delay or some acceleration.
Another thing weird about controlling the bird is that it behaves like a plane when it loses speed, it starts falling backwards first while a bird would lower its front to keep balance and THEN start falling down, by tipping the front down. I'm just saying that it doesn't feel natural. It works if I imagine the bird being some sort of realistic, animate kite or a paper craft, but if it's a real bird then it's kinda weird.
Just sharing my thoughts. I really like games like this and I wish I could enjoy it more, just from the comments I think it's more of a problem with me than with the game but still, I think it could have been done a bit better and you'll try experimenting with different controls next time! Cheers!