Rock just told me he had seen this thread.
Errrrrrr... not sure what to do really. The bird is prolly in shock right now which is why it isn't flying - you know like when they fly into a window and knock themselves out. Keep an eye on him for a bit. If he falls down then, me, I would pick him up and put him in a box for a couple hours, close it so it's dark and quiet and see how he responds. Put a little water in the box. If he flaps around, then open the box somewhere safe and turn it on it's side so he can get hop out.
Mis - if the boid can't fly, nature will takes it's course. If he stays in the box and looks a little folorn - maybe check back to SheW thread about her little blue jay.
I don't know how quickly or if big feathers regrow- I'm sure they can survive without some of their feathers, especially the top part of its back and if the wings aren't broken he may just fly off. If you do bring him down it may be better to keep him safe for a few hours til the bleeding stops and he's less vulnerable.
Do you have an animal shelter you can make a phone call to, or the vet - and ask their advice? Back home we take any wild animals down to the vet and once they are ready to go back in the wild they vet releases them.
I reckon if the wee fella is in the tree and is sitting there, best leave him there for a bit and see whether or not he tries to fly. You may be surprised and he make take off. If he drops down, try the box thing. They calm down in the dark and quiet and re-orientate themselves (had a rookery - know the feeling - it's sad when they are struggling).
Maybe PM the lovely Mr Patiodog in case he checks in this morning - he'll know what to do and always give sound advice.