Legend has it that the Stephens Island wren was the only species driven to extinction by a single living creature. The culprit? A cat named Tibbles, a pet belonging to Stephens Island lighthouse keeper David Lyall. The wren was endemic to New Zealand and was one of the world’s only known species of flightless songbird. The story goes that, between the time the Stephens Island wren was first discovered on Lyall’s doorstep in 1894 and the time it was confirmed as a new species, Tibbles had succeeded in killing every wren on the island. Because of a history of habitat loss and predation by the invasive kiore (or Polynesian rat) on the mainland, Stephens Island had been the wren’s final sanctuary. By 1895, less than a year after its discovery, it was extinct.
While the legend’s accuracy is doubtful—Tibbles, if he ever existed, likely had a handful of non-native feral accomplices—no one denies its conclusion. The story is a familiar one in New Zealand. In the roughly 700 years since humans first settled New Zealand, at least 51 species of native bird have gone extinct. Invasive species have wreaked a radical and damaging effect on the evolutionarily unprepared. Many of New Zealand’s native birds were unarmed and flightless, defenseless in the face of the new wave of predators landing on New Zealand’s shores. Now, New Zealand’s Department of Conservation (DOC) is taking innovative steps to save birds besieged on the mainland: it is relocating endangered bird species to small offshore islands engineered to recreate the conditions of New Zealand seven centuries ago. I witnessed firsthand the success of the DOC’s efforts on Tiritiri Matangi, one of the most promising and accessible of these islands, where some of the world’s rarest birds can be found in flocks.
For millions of years, plants and animals living in New Zealand evolved in total isolation from the rest of the world. When humans first reached the islands around the year 1300, they encountered creatures unlike any they had seen before. Imagine being the first person to see, for example, the giant weta, the world’s heaviest insect, a massive wingless cricket that can weigh up to 70 grams, about the weight of three adult mice. Or picture roaming the forests at night and stumbling upon a kiwi, a miniature relative of the emu with nostrils at the end of its long, thin beak, no visible wings, and fluffy brown feathers that look like a coat of fur.
Because of New Zealand’s great distance from any other large landmass, the only organisms capable of colonizing the islands were those that could fly or float to their shores. As a result, no mammals, except two species of bat, are native to New Zealand. In the absence of mammalian predators, many New Zealand birds gradually lost the ability to fly and took to foraging on the ground. These strange birds—the nocturnal kiwi, the grazing takahe, the giant moa, the kakapo, and others—flourished in ecological niches elsewhere occupied by mammals. Birds in New Zealand were the grazers, the scavengers, and the predators. But with the arrival of humans and their living cargo, the heyday of the New Zealand bird came to an abrupt and unceremonious end.
The impact of Polynesian settlers was quickly felt by New Zealand’s rare biota. Men capitalized on the readily available food source supplied by millions of years of evolution. Big, flightless birds unaccustomed to land-based predators made easy prey. After only a hundred years, the once-abundant giant moa had disappeared and, with it, its primary predator, the Haast’s eagle—the largest eagle ever to exist. Rats, stowaways on Polynesian boats, quickly made themselves at home in New Zealand’s untouched landscape. Their insatiable appetite for eggs makes them a continuing scourge for New Zealand’s bird populations. Today, there remain only about 120 kakapo—a large, nocturnal, and flightless parrot—all now on predator-free islands. About 500 years after the Polynesians, Europeans settled New Zealand, bringing with them a Noah’s Ark jam-packed with invasives: deer, moose, cats, dogs, more rats, rabbits, wallabies, and Australian possums for the fur trade. When rabbit numbers exploded, weasels, stoats, and ferrets were released to bring populations under control. But the Europeans then lost control of their “biocontrol”: stoats and their fellows found New Zealand’s slow-moving endemic birds to be easier prey than the rabbits and hares. Stoats, together with deer, rats, cats, and possums, pose an ongoing threat to what is left of New Zealand’s unique biological heritage.
The Department of Conservation is now attempting to save New Zealand’s remaining indigenous species. In 1984 the DOC and a legion of volunteers belonging to the group “Supporters of Tiritiri Matangi” undertook a large-scale restoration project on Tiritiri Matangi Island, which had been cleared in the 1800s for farmland. In the decade that followed, more than 300,000 native trees and shrubs were planted. The plan was to transform Tiritiri into a refuge for New Zealand’s disappearing birds. But before birds could make Tiritiri their home, invasive mammalian squatters had to be removed. Because of their modest size and isolation from the mainland, Tiritiri and other small, offshore islands present a unique opportunity for conservation and management. While it is almost impossible to eliminate rats, for example, from any part of mainland New Zealand, the DOC can completely eradicate a small island like Tiritiri relatively quickly. And after the island has been cleared of invasive pests, careful management can prevent the reestablishment of unwanted intruders. In one helicopter drop in 1993, the DOC poisoned every rat on Tiritiri Matangi, making the island officially mammal-free.
I arrived on the island after an hour-long ferry ride from the mainland. Even in my first few minutes there, standing on the rocky beach and half-listening to the park ranger read us the rules, the island around me seemed to be humming with life. Thick growths of green flax, the plant used by the native Māori to weave mats, baskets, and rope, lined the beach, their long leaves rustling as small birds darted between them. Bright flashes of living color caught my eye: two kingfishers—pale yellow chests and glittering blue backs—were flying close to the water. Once free to explore, I hiked into the shaded interior of the island, walking on the wooden walkways set up by park volunteers. At first, I was thrilled just to catch a glimpse of a red-eyed, olive-colored bellbird, a small songbird famous for its ringing song often punctuated by grunts and wheezes. But as I moved deeper into the island’s forested center, where the pohutukawa trees grow gnarled and the leaf cover thickens, the bellbirds were everywhere and the sparse, lilting birdsong of the shore gave way to a thunderous cacophony. It was a startling sound: what seemed like dozens of different threads of song garbled into one raucous chorus. I approached a water trough in the green shade and was surprised by a tui, the largest member of the honeyeater family (the same family of curved-beaked birds to which the bellbird belongs). The tui’s feathers looked black until the sunlight revealed their green iridescent sheen. The tui was unlike any bird I had seen before: a tuft of bright white feathers puffed out from its throat and a lacy collar of delicate white stood out against its dark coloring. While I was acquainted with New Zealand’s ubiquitous Tui beer, I had never seen its namesake, a songbird that can mimic the calls of other birds and even the human voice. Just moments later, a North Island kokako, one of New Zealand’s most bizarre and endangered birds, landed in a tree behind the trough. The kokako was one of the twelve species of endemic bird relocated to Tiritiri after rats were removed. The sleek, slate-gray bird with bright blue wattles is known for its beautiful calls that some liken to organ music. Because of its short, stubby wings, the kokako prefers hopping instead of flying through the trees. On its perch behind the trough, the kokako was bobbing its head and flapping its little wings—a type of courtship behavior, I’ve been told, called an “archangel display.”
The trail eventually led me up out of the dense canopy to a grassy hilltop from which I could see the distant volcanic peak of Rangitoto, another island in Auckland’s Hauraki Gulf. Scattered around a whitewashed lighthouse, one of the island’s few manmade structures, were purple, green, and blue birds with oversized scarlet feet. Takahe weigh an average of six pounds, making them the largest members of the rail family. These flightless birds are New Zealand’s version of the cow, and they graze with the same tireless dedication. When I saw them, most of their red beaks were bent to the grass. I crouched down close to one of them—close enough to reach out and touch it—and the bird, entirely unruffled by my presence, kept feeding. The endemic takahe was believed to be extinct until it was rediscovered in 1948. Just 270 takahe are alive today with a population of 13 birds on Tiritiri (in 2008 stoats killed 70 takahe in the Murchison Mountains on the mainland—a devastating blow to the species). More than half of all takahe are now on offshore islands. Every takahe on Tiritiri has a name and is carefully managed by the DOC. While takahe are practically impossible to encounter in the wild, they are literally underfoot on Tiritiri Matangi: I narrowly avoided tripping over one while it begged for scraps from my lunch. At the visitor center on the hilltop, I found an old woman scolding a takahe named Greg who was trying to barge his way inside.
On my hike back to the ferry, I stayed close to the coastline. Just inland from the water, I came across a wooden nest box on the ground. I lifted the top and found two little blue penguins peering up at me. The blue penguin is the world’s smallest penguin and is native to New Zealand. It fishes in the open water all day and rests on land at night. Nest boxes provided by Tiritiri volunteers are a coup for penguins and visitors alike: ready-made housing for the penguins and, for the tourist, a rare opportunity to see these seabirds up close.
Tiritiri is one of over a hundred pest-free offshore islands used for threatened species recovery by the DOC, which is currently in the process of eradicating invasive mammals on two more islands in Tiritiri’s neighborhood. For birds like New Zealand’s little spotted kiwi, a species of kiwi extinct on the mainland due to predation by invasives, these island sanctuaries are truly a last resort. Breeding efforts and rehabilitation of endangered species have been so successful on Tiritiri that the island routinely exports rare birds to other offshore island projects. Researchers from around the world visit Tiritiri to study and try to replicate its success.
Predator-free islands are not a wholesale solution to the damages wrought by invasives. It has proven to be almost impossible to eliminate mammalian pests on the mainland, although management strategies similar to Tiritiri’s are being deployed in geographically isolated or fenced-off mainland islands. The DOC’s work on Tiritiri and other such islands may therefore make the difference between existence and extinction for many New Zealand birds. Tiritiri Matangi not only protects and rehabilitates disappearing species; it is also a living museum of natural history. It is an opportunity for people to experience New Zealand as it might have been 700 years ago, before cats, rats, and stoats, when forests were thick with pohutukawa and birdsong.