Very cool game! I really enjoyed being a bird and flying around. It has a fantastic sense of momentum and I really enjoyed the challenge of flying around. Your use of physics to govern the bird's flight-path adds a lot to the game and there's a lot of mastery involved in flying.
The controls were a little confusing to me. I needed to do the tutorial and afterwards I found it hard to grasp the the idea of holding one direction while tapping the other, I wonder if this could be simplified? Maybe you could always flap by tapping buttons, even without holding the other key? Still, those controls are a minor problem overall. It's a fun game with a chill vibe and a fantastic sense of movement and velocity. Well worth expanding on!