Once I got the mechanic, I was determined to keep getting better with each try. You plugged into that gamer itch to keep going. All of the menus were clear and easy to access. The song worked great for the game. As a small suggestion, consider some kind of visual when the bird crashes (screen shake, cartoony explosion, leaves bursting in the air) along with audio for the bird itself. Every 25m on the distance could also giving a rising audio indicator, so the player knows they just hit a milestone. If you are going to keep going with this game, consider a visual representation of the upgrade on the bird itself (for example, he gets sunglasses or a cape, when he gets more efficiency). Very fun game loop!