This was a rescue with a sad ending. Seems our own cats may have done this dastardly deed. We gave it a safe space, food snd eater when it could, for a few days. Seems though, that there was a neck or back break. Poor thing never regained control of one side. So, maybe a stroke, I suppose birds have them, but given the way cats kill, my money is on the spine or neck.
Either way, he was pampered, not shredded and eaten, for his end. I suppose there is that.