Probably a good idea to just cull :)
Mossypath, I didn't see your comment about the rabbits - wry neck occurring in rabbits is almost always due to a pasturella infection that has spread to the inner ear. Rabbits are natural carriers of pasturella but get ill when their immune system can't...
sorry forgot this link too: this a guinea hen with the same clinical sign but infected with Newcastle: http://partnersah.vet.cornell.edu/avian-atlas/search/disease
I don't know about in the states but in Canada Newcastle is a reportable disease - I would watch your other birds carefully and do...
The medical term for this is called opisthotonus - the head bent straight back. There is another term for the head going wry at a lateral angle: torticolis. The first thing that came to my mind was Newcastle and Marek's as this can be one of the clinical signs. Here's what the Merck Veterinary...