They're mostly suplus stock or quarantine. I've only been in one of the service yards once, when a kind worker let us see the bat-eared foxes before they went on show. They, and the other animals I saw which I remember being Black-and-White Ruffed Lemurs and Sun Conures, were kept in cages similar to the ones behind the gibbon complex (now off-show enclosures themselves). The behind-the-scenes enclosures are the stable yard behind Tropical World where I saw the foxes, the mentioned avairy row behind the gibbons and a few yards in the strip opposite the play area. In the future, the plan is to create one big service yard on the site of the wild ass/roan paddocks with a viewable vet centre, allowing Tropical World and the Boreal Forest biome to expand.