Unlikely to have been bred, rescued or even to be released. I felt this was just a standard bird on display at the zoo. It may have been injured initially, but I couldn't see anything obviously wrong when I saw it. This single specimen was on its own in a small cage at the zoo. (I'll try and upload a photo.)
The zoo frequently have some large seabird on display, I don't know how they get them though.
To have a single young bird is odd (and makes ID significantly more difficult).
