Rangatira — a key nature reserve

Forest and Bird, Volume 16, Issue 4, 1 November 1985, Page 14

Rangatira — a key nature reserve

Alison Davis,

Few mainlanders ever have the opportunity to visit the Chatham Islands, a windswept group of two large and more than a dozen smaller islands about 870 km to the east of Christchurch. And yet these remote islands are among the most important for our native flora and fauna.

a research

student at Auckland University, outlines in this article the significance of Rangatira, or South-East Island. Only 218 hectares in size, the island nevertheless harbours a large number of endangered bird species, as well as rare insects and plants.

R angatira Island (South-East Island) must rank as one of the most important of New Zealand’s nature reserves. All the bird species recorded by ornithologists in 1871 are still present; only on Rangatira are the rare New Zealand shore plover and the Chatham Island petrel found. Thirteen of the 15 endemic Chatham Island birds, the Chatham Island skink, numerous endemic insects and two-thirds of the endemic Chatham Island plants make their home on the island. The reason why Rangatira abounds in wildlife is simple: there are no rats on the island. Incredibly, no rats became established from ships that called in during the whaling days, and no exotic animals remain today. Humans first came to Rangatira more than 700 years ago. The Moriori used to collect seabirds and eggs, but they did not live on the island, and today no sign of their presence remains. European sealers and whalers arrived in the early 19th century, and a whaling station was established in 1880. Sheep, cattle and goats were introduced during this time and the goats soon reached epidemic numbers. Until 1957 the island was farmed, with the last sheep removed by the Wildlife Service in 1961. Today the birds, insects and plants have the island to themselves, except for the occasional company of human beings

who come to observe them. The forest is regenerating to the extent that it is almost the same as when man first arrived. Endangefed birds The rare Chatham Island petrel spends most of its life far out in the Pacific Ocean, but during the breeding season returns to its nesting burrow at night. Petrels have an uncanny ability to fly directly to their burrows without losing their way. Once widespread in New Zealand, by the 1880s the colourful shore plover had become restricted to the rocky shore and salt meadows of Rangatira, where a population of 120 now remains. Its habit of nesting under vegetation made it vulnerable to mammalian predators. This appears to be why it disappeared from mainland New Zealand and Chatham Island. The best known of the Chatham Island birds is the celebrated black robin, which has increased its numbers to 38 from a low of seven. In 1982 some were transferred from Mangere Island to Rangatira, where the better forest has given the population an opportunity to expand. A semi-nocturnal bird of tussock and forest, the Chatham Island snipe — the smallest of New Zealand’s snipe — had at one stage disappeared from all of the Chathams except Rangatira. In 1970 it was successfully re-introduced to Mangere. The bird’s unusual aerial display, and the sound made during this display, has given rise to Moriori legends of a large mythical bird. The forests on Rangatira support all

the forest birds of the Chathams except the Forbes parakeet. The Chatham Island parakeet is especially common; I saw many of their nests in holes in the old stands of akeake (Olearia traversit). At night the forest is alive with the sound and movement of thousands of nesting seabirds, whose burrowing has left the forest floor bare of most vegetation. Rangatira is the main breeding ground for the broad billed prion and the white-faced storm petrel — more than a million pairs of the latter breed on the island! One of the world’s smallest seabirds, the storm petrel is not found on any island with mammalian predators.

The extensive rocky shore is important, not only for the shore plover but also for the Pitt Island shag and Chatham Island oystercatcher. Of 50 surviving oystercatchers, half are on Rangatira and it appears that only these birds are breeding successfully. Scurrying and jumping insects Pitt Islanders are familiar with the large, hairy spiders of Rangatira, but not so well known are the island’s unusual insects. Of particular interest are several large flightless insects — a weevil and click beetle. Because the weevil lives on the endangered Chatham Island speargrass (Aciphylla dieffenbachi), its survival is in doubt. At night, the forest floor is alive with scurrying cockroaches, beetles and jumping wetas. The two species of weta present differ from their mainland counterparts as they are cave wetas. On warm, sunny days the brightly coloured Chatham Island red admiral butterfly flits among the muehlenbeckia and bracken. The Chatham Island skink is common in tangled vegetation. It can be seen and heard scurrying through the leaves when one passes by. Our ‘‘Cook’s tour’’ of the wildlife of the island finishes up on its southern shores, where the largest colony of fur seals in the Chathams is found. In the summer months bulls guard harems of females whose pups bask and play in the sun. Gnarled forest trees The Chatham Island forests are unique, with most of the forest trees endemic. On Rangatira the gnarled akeake trees (Olearia traversit) grow on the exposed coastal niches, while Myszne chathamica and Chatham Island lancewood and ribbonwood flourish in more sheltered areas. During summer droughts the ribbonwood trees lose their leaves. Such semi-deciduous ribbonwood forests are unusual in New Zealand. Most of the south coast is salt meadow, which is regularly showered with salt spray during strong southerly winds. In spring, the meadow is a sea of pink iceplant flowers, with splashes of yellow, white and purple from Cotula, sea primrose, cress, the creeping Hebe chathamica, and Chatham Island geranium. Away from the salt spray Poa chathamica and Carex trifida form a dense tussock sward in exposed places. Scattered among this are the endangered spearerass Aciphylla dieffenbachit, the giant nettle (Urtica australis) and the spectacular Chatham Island forget-me-not. These giant herbs are also found on the steep cliffs and summit with the _ purpleflowered Olearia chathamica and Hebe dieffenbachi scrub.

Hold breath and hope Botanist David Bellamy, in the foreword to the recently published book, Black Robin Country, writes in reference to the black robin that ‘‘ New Zealand holds her breath in hope.’’ The same can be said of Rangatira Island. The greatest threat to it is the accidental introduction of rats. If these vermin arrive we would certainly lose the New Zealand shore plover, the black robin, snipe, the Chatham Island oystercatcher and petrel, along with millions of seabirds, the skink and many rare invertebrates. To quote David Bellamy, if all these animals become extinct, it will indeed be a black day. ‘‘And so the world waits with baited breath...."’ we