Hey Phil,
How very impressionist of you!
I kind of like the approach, while also wondering how a more straightforward description would've come out. If you did try that, I could see a potential combination of the impressionst fragments and regular description potentially working well.
Anyway, keeping to what you have here, how about introducing more line breaks to make it feel that bit more erractic, reflecting the experience of the bird? e.g.
membranse slashed shell cracks
hunger
untethered
again
nest clinging
in the cleft
of a white cliff
Apart from that, I thought the last verse wasn't needed. While I appreciate the ambition of the sulln rock, it felt a touch too far to me.
I could feel the experience of the bird pretty well, I thought, so well done.
Trev