The bird movement is really good. I still do think that sometimes the initial boost is fast, like I'm not sure what exactly is the time need to go into flow state, I like the different turns at varying speed. I love the dink when you hit something at really high speed. This sort of reminded me of Haste, with it's visuals and it's focus on speed. Though it's much more forgiving and I do like that. The levels are simple enough where you can fairly easily find where to go and I believe they might be placeholder at the moment anyway.
I'm not sure how I feel about there being a single jump, I do think it adds to the level design of the game but I also want to spam it for some reason. I think an upgrade could be something for it, where you can upgrade wings to get double+ jump.
The sound effects were fine as well but I do think they could be improved upon.
And overall I think it's a fine Demo for a bird game, the movement is nice, the bird model itself is pretty good and it looks nice visually as well.