From the Clore Pavilion, London Zoo thread: I hate to contradict you grantsmb , but there's a great example of this with GLTs free-ranging throughout a large portion of the National Zoo in Washington DC. National is a free zoo, and has a very high visitation, and DC is hardly as genteel and cultured as Jersey (although parts of DC are truly lovely - sorry any DC readers!). The GLTs have night boxes throughout the trees, and of course, have access to heated indoor areas at night. There are ropes strung between a number of trees, so the animals have a large area to roam around. To my knowledge, there have never been any escapes or thefts of these animals at National. The international studbook keeper for GLTs works at National Zoo, and if there was any hint of a problem, I'm sure he'd push for an end to free-ranging GLTs.