like zacsmaster says you need to ask the council or whoever actually runs the site, we're not allowed to but one year a chap took over one further down from us and had chickens, rabbits & a couple of geese! the geese mysteriously disappeared after a few weeks (never asked what he'd done with them!) but one morning went up mine and half the chickens and rabbits were lying around on my allotment half eaten & it was a horrible sight! obviously the foxes had managed to get into the pens & had a feast. so if you are allowed, security for them must be a priority, (urgh! even now when i think back to seeing them that morning it makes me shudder :-(