The last time I was on Tiritiri Matangi, the bird sanctuary in the Hauraki Gulf off Auckland, I noticed a bunk house. This facility is run by the DOC (Department of Conservation), so you can stay on the island. Staying in the bunkhouse is in high demand as it is popular among volunteers staying on the island, but it is also for bird-watchers as nocturnal birds cannot be seen during a day trip.