Coding your own physics engine for this is really wild stuff. The whole thing functions surprisingly well and bird always seems to find ways to correct herself.
Love the model, she's very expressive. The breathing and blinking animations go a long way towards making the character feel like more than just a ragdoll. The only thing I don't like is the little tuff of feathers under her chin which I mistook for a second mouth while she was dangling upside-down. Though I do love the low-poly aesthetic, since the game's all about getting in close and trying different poses, increasing the poly count and texture resolutions might make sense.
I don't mind the lack of sound given the way the game is set up. Some background ambiance and feather ruffling sounds might be nice, but I don't think they're fully necessary.
I don't know what your future plans for this project are, but the whole thing is an explosive barrel of potential right now. I would personally just love to see the game expanded with more interaction options and characters, but I'm also not the sort of person to hand-build a physics engine, so my horizons aren't all too broad. Drag funny bird fun, want drag many bird and do many more thing.