Interesting mechanic with the slow falling bird. Makes it different from usual platformers.

is it an interesting mechanic

Really nice! I loved the graphics and aesthetic. Controls felt pretty good and I liked the puzzle platform designs! The one-jump mechanic was really interesting! You definitely designed the levels well around that limitation. 

I didn't quite finish the game but I think I got pretty far. The death stuck bug caught me a few times and I didn't want to restart again from the beginning (R button didn't work for me either).

I think my main feedback is around the first checkpoint, if you miss the first feather jump, you have a long path to backtrack and get back to the checkpoint.. but it's just faster to jump into the electricity and respawn. I think if this was the intended punishment, missing the jump should just drop you directly into electricity and respawn you.

I also got stuck on the first cannon part wayyy longer than I want to admit lol. You'll see me struggle in the video for a while :P

Really great job and I'd love to come back to play again with some of the soft-locking bugs fixed :)

I really liked the screen transition effect too!

Visually and audio-wise, this is very impressive and I hope you continue to polish this game!  You nailed the theme of the game right on as well.

Nits:

• It took me forever to figure out how and when to use the Z key.  Clearer instructions on your game page would help.
• Sometimes with a screen scroll, I would get another bird added to my roster of birds, plus other items like feathers would double, triple up, etc.  This would cause a lot of clutter and a fail when hitting something bad.
• Dang, those are some POWERFUL feathers when doubled, tripled up, etc.  They would send me through more than one screen and right into a wall :O

I have caught comments on the R key.  It did do something for me.  The shake at the start of the game was  mildly entertaining.

I think a bit of cleanup on code is called for.  Otherwise, this is a very solid start and is worth developing more when the jam is over.

Cute little game! The challenges feel a lot like Celeste. Also, the feather is very satisfying.