The locals, though, more than toe the DoC line. On a Village and Bays Tour with cheerful Kimba, I learned there were a swag of conservation groups working together on the island, not all of them domestic.
At Horseshoe Bay, for example, with its perfect sandy curve, she pointed out the predator fence across a peninsula of regenerating bush erected and maintained by the California-based Dancing Star Foundation.
Fortunately, there have never been mustelids, mice or pigs on the island but cats, rats and possums require constant vigilance.
An unusual addition to the bird population when I visited was a kotuku, or white heron, that was stepping gracefully through the shallows of Mill Creek, hunting fish and causing some excitement amongst the islanders.
"So rare here!" breathed a burly birder, reaching for his big lens. The pilot on the Paterson Inlet cruise to Ulva Island got a thrill, too, when the blue penguin he thought he had found for us turned out to be the much less common yellow-eyed one.
"Haven't seen one of these for so long," Josh said happily, backing up the boat for a second look to the confusion of the stern-looking albatross that had skidded alongside for a feed of fish frames.
Ulva Island itself, a short cruise from Oban and completely predator-free, is alive with birds.
A guided walk through the bush had us spinning in circles to see the robins, kakariki, kaka, tomtits, tui, bellbirds and woodpigeons that are just some of the species living there.
Sadly, the Stewart Island brown kiwi was a no-show.
Unlike most other kiwi, it's active during the day and people on the tour who had just walked the three-day Stewart Island track reported that one had come right up to them in broad daylight on the beach at Mason Bay.
The next best thing to that was to go on one of Phillip Smith's kiwi-spotting tours, to catch the night-shift feeding on Ocean Beach, a half-hour by boat from Oban.
After a full briefing on kiwi facts on board, we followed guide Greg by torchlight through the bush, stopping when we heard the hoarse screech of the male and then the squeak of a female.
Though there are no guarantees of a sighting, when we got to the beach the torches showed up unmistakable footprints fresh and clear in the sand, and a real, wild kiwi at the end of a trail - so busy feeding that she took no notice of us standing just five metres away.
The tideline was heaped with kelp seething with sand-hoppers, and it was these that the kiwi was probing for, thrusting the full length of her beak deep into the sand. It was thrilling to see this icon in its own environment, behaving normally and fending for itself, and recognising just how remarkable it truly is.
On the way back, enjoying a midnight hot chocolate, everyone was buzzing and sharing their photos, all of us delighted with the evening's success.
We had seen three kiwi on the beach, of an estimated island population of 25,000 altogether, which is more than in the entire North Island - and probably good reason to give DoC its due.
CHECKLIST
Getting there: Fly from Invercargill with Stewart Island Flights or take the ferry from Bluff.
What to do: Village and Bays Tour; Paterson Inlet Cruise; Bravo Adventure Cruises' Kiwi Spotting Tour.
Where to stay: Bay Motel in Oban.
The writer was hosted on Stewart Island.
