The artstyle is very unique, but it did strain my eyes after a few minutes. Controlling the yaw, pitch and roll of the bird was ok, but the artstyle makes it very hard to orientate the bird with respect to the world's horizon. The effects for catching the wind was a nice indicator that I did something right. But it would also occasionally obscure the entire screen, which contributes to the orientation issue.
I like that you can manually flap the birds wings to increase the bird's speed. However, it didn't feel as though gliding around is possible as I would "stall" and drop straight downwards if I stopped flapping the wings.
The ability to control flap speed usage through adjusting the heart rate is interesting. However, I was unable to discern any noticeable effects when adjusting the heartrate, except for a louder heartbeat. The increase in this sound effect's volume was useful for reducing the number of things that I have to visually focus on, so it was a good piece design.
Difficulty-wise, it would be easier to start on land due the amount of available landmarks that would help orientate the player. If you were to include any waypoints or markers, a home marker for the nest would be useful.
At the moment, the flying aspect feels clunky and that is what is holding it back. I do think that there is potential but it depends on refining the flying mechanics.