The onager family once kept behind the scenes in the off-site breeding center. The zoo recently started the long-overdue renovation project of the breeding facility, which is why they’ve been moving around the animals (they probably put the black-necked cranes on exhibit for the same reason). The project is the sole priority for the zoo at the moment, and it could take years before their other planned projects (bear, hippo, new reptile house, etc.) to materialize.