Sanctuary in the chathams

Forest and Bird, Issue 296, 1 May 2000, Page 28

Sanctuary in the chathams

DEAN BAIGENTMERCER explores Mlangere Island's tragic past, and its present conservation

angere Island lies in angry seas, remote from the mainland of New Zealand, yet its role in saving endangered species is internationally known. Since Forest and Bird substantially funded its purchase in 1966, the island has become the last refuge for several of the vanishing species of the Chatham Islands. Among them is the black robin, once the rarest bird in the world. Tiny Mangere Island (113 hectares) lies just off Pitt Island in the Chathams group, 800 kilometres east of Lyttelton, on the way to South America. A choppy and swift 100 metres of sea is all that separates Mangere from its sheer-sided sister, Little Mangere Island — famous for being the home of the last five black robins. The dramatic rescue of these birds, and the establishment of a breeding colony on Mangere itself, has become a classic tale of conservation history. Both Mangere and Little Mangere are the eroded remains of ancient volcanoes poking out of the submerged Chatham Rise. Unique wind-sculpted forest once grew up to the edge of Mangere’s bluffs, while lush coastal herbfields adorned the cliffs. Hundreds of thousands of seabirds dug their burrows to breed here, enriching the earth with their nutrient-abundant droppings. Moriori hunters must have found a noisy forest by night and day with constant bird banter about the heavily bird-bur-rowed forest floor. A naturalist, Hugh Martin, called for the urgent protection of the ‘Mangere rail’ — among other birds — in 1885. The rail had existed elsewhere on the Chathams but by then was forced to extinction except for the last remnant population on Mangere Island. Farming settlers began burning Mangere’s forest just two years later. Only three to four hectares of forest survived the flames. Then, sheep, goats and rabbits were released on the island. When rabbit numbers exploded, cats were introduced to lower the population. But the cats’ success went well beyond wiping out rabbits — black robin, Forbes parakeet, Chatham petrel, snipe and the last ‘Mangere rail’ also disappeared. Alan Tennyson, Curator of Birds at Te Papa/Museum of New Zealand, has examined bird fossil deposits from Mangere and estimates seven or eight bird species may

have become extinct from Mangere Island before 1872, and another nine to 12 by the end of the twentieth century. Some of these birds survived elsewhere, and a few have been re-introduced to Mangere Island in recent years. Others, however, are now totally extinct. Mangere Island bird bone deposits have revealed two species of rail (relatives of weka), an unnamed shelduck, a gadfly petrel, the Chatham crested penguin, snipe, a kaka and a bellbird all distinct from their New Zealand relatives. All were once present on Mangere, and other Chatham Islands, but are now totally extinct. Remarkably, no rodents, possums, weka, or mustelids (ferrets, weasels or stoats) were ever deliberately or accidentally liberated on Mangere. By contrast, most of Chatham Island, and Pitt Island, have been cleared for farming. Those islands now have many animal pests including rats, possums (both absent from Pitt Island), mice, feral sheep, pigs, cattle, and even horses. ous contribution’ toward the Crown’s purchase of Mangere Island as a reserve for flora and fauna. At the time Mangere Island was reported as still being farmed, with birdlife ‘limited mainly to gulls, petrels, and other seabirds’. After cats were removed, Chatham Island snipe were successfully re-introduced in 1970. During December, their fluffy ‘ping-pong-ball’ chicks can be seen, loudly peeping, following a parent. As the patterned feathers of these small birds blend perfectly with leaf-litter, spotting a snipe is usually easiest when it blinks. In 1977, the famous population of the last five black robins, including only one breeding female, was removed from Little n 1966, Forest and Bird made a ‘gener-

‘Megaherbs’ on Mangere T= Chatham Islands have 388 plants native to the group. Some 47 species (12 percent) are found nowhere else. Many trees common in the forests of New Zealand, such as beeches, podocarps (rimu, kahikatea etc), manuka, kanuka, rata, and cabbage trees, are naturally absent from the Chathams group. Some of the most threatened plants are those of the coastal herbfields which germinate in the loose fertile earth around bird burrows. Notable are the kopukapuka/ Chatham Island forget-me-not, punui/soft speargrass Aciphylla dieffenbachii, shrubby button daisy Leptinella featherstonti, an unnamed Cook’s scurvy grass, and the giant sow thistle Embergeria grandifolia. Although New Zealand gardeners bribe their Chatham Island forget-me-nots with shade, salt water and seaweed, those on Mangere Island exist in the most extreme of circumstances: full sun, often on seemingly vertical cliffs exposed to the brunt of salt-laden gales. They grow very large — their leaves at least as big as rhubarb — and lose around a third of their foliage during the dryer months. Goats previously ate these plants off every accessible spot. Decades after the goats have gone, plant populations are showing signs of recovery, thanks to the strong winds frenetically dispersing the large seeds.

Slow march of the speargrass weevils peargrass weevils aren't very S= In fact, it would be fair to say they live life in slowmotion. This doesn’t prevent the weevils from consuming whole patches of soft speargrass, however. During research for her PhD, Katrin Shéps marked and studied 10,000 of Mangere’s weevils for three to four years. The weevils and their larvae consumed a whole population of soft speargrass (above and below the ground) until there was not a single plant left alive. After this orgy of gluttony, marked weevils were found up to 800 metres away on further speargrasses, which may sound of no consequence until you consider the painfully slow way they move. This boom-and-bust cycle may be typical of the dynamic lifestyles and co-existence of these weevils with soft speargrass. Several years later, the studied speargrass population is recovering. With both the plant and its predator nearly extinct from the main Chatham islands, due to farming of habitat and rat-browsing, Mangere is one of their last remaining strongholds.

Mangere Island to Mangere Island. Today Mangere shares the world population of around 250 with nearby South-East Island. With Mangere mammal-free (with the exception of occasional human workers), the Wildlife Service embarked on a visionary plan of full habitat restoration which is continued today by the Department of Conservation. One main incentive for returning the forest to the island was for Forbes parakeet, which naturally exists only on Mangere and Little Mangere. It is thought Forbes parakeet was a forest dweller, while another kakariki, the red-crowned parakeet, favoured the bush fringes. However, without the forest, both species hybridised, bringing Forbes parakeet close to extinction. The replanting of forest is intended to again provide separate habitats for these two species of kakariki. Habitat restoration has included decades of replanting akeake and flax as shelter for the initial phase of forest recovery. It may sound simple but today’s revegetation programme is a complex affair on which DoC’s botanist for the Chatham Islands, Amanda Baird, has spent years experimenting, monitoring and improving. Currently, the planting regime takes the following course: seed mostly of akeake and additional berry-producing natives is collected in summer and grown on Chatham Island for 16-17 months, until big enough to plant. Thorough inspection takes place during packing to ensure no rats or garden snails hitch a ride. Some 6000 plants are then ferried by fishing boat to Mangere Island each May. Local planters then work dawn till dusk carrying the young trees over demanding terrain, often in challenging weather conditions, to their own pre-sprayed patch for planting. All 6000 trees are weeded seven months later to ensure a high percentage survive — then they’re on their own. Two plants from Mangere’s original forest are absent still: the endangered Chatham subspecies of nikau palm and the supplejack vine. These plants may need to be reintroduced manually by conservation workers. As yet the parea (the endangered Chatham Island forest pigeon), with its ability to disperse large seeds as ‘fertilised deposits, has not returned to Mangere. The absence of rodents has ensured an interesting insect fauna remains. Two species of cave weta, abundant at night,

venture right down to the shore line, and speargrass weevils chomp their way through the night (see boxes). Also nocturnal are the sloth-like Chatham giant stag beetles. The males are easy to identify by their large mandibles extending in front of the head. Female mandibles are much more reduced and subtle. By day, giant stag beetles hide from the light in patches of thick organic matter, alongside their larger larvae which at a quick glance look like C-shaped, blue-grey huhu grubs. Rain brings out giant slugs, up to eight centimetres in length. These rubbery grey-ish-black creatures look more akin to a toy-shop fake slug. They can be seen sliding about akeake trunks and among flax fans. One of our largest spiders, the rangatira, lives here. With legs four to five centimetres long, and egg sacs the size of a glass marble, these spiders prey on weta. They also seem to have a fetish for cylinders, often making themselves known at inopportune times, such as when one reaches for a mug or for toiletpaper. Rangatira spiders seem to have a variety of colourings, and are a velvety purple underneath. On cloudless days, the Chatham subspecies of the common skink can be found

in abundance, sunning themselves. Their bodies shimmer as they escape through giant sedges. Most have tails at various stages of regrowth after having them nipped while venturing into bird burrows. Their sleek reptilian skins are a diversity of colours: pounamu green, sandy brown, shiny black, whitish-green, dark brown, even salmon pink. The endangered Chatham Island oystercatcher has been re-introduced successfully to Mangere, and the Department of Conservation is working towards the reintroduction of shore plover. Once a common coastal bird of the Chathams and New Zealand, shore plover are now reduced to two remnant populations in the Chathams, and a handful of experi-

mental sites for reintroduction in New Zealand. With much of the Chatham Islands group cleared of forest and affected by pests, Mangere is an essential sanctuary for the survival of many unique birds, spiders, insects and plants. Since its purchase as a reserve, Mangere has become an ark of international significance.

DEAN BAIGENTMERCER co-manages the urban Wellington forest restoration project and is national spokesperson for Native Forest Action.

I love the nightlife s the December sun disappears behind the long, flat sliver of Chatham Island, 60,000-70,000 muttonbirds return from a day feeding at sea. Looking like a swarm of bees, the sooty shearwater, or titi, circle around the top of Little Mangere. Within 20 minutes these black-brown birds with purplish feet are crash-landing into the vegetation of the two islands. Unlike the pipits and gulls, titi have never mastered the art of landing gracefully nor practically; they speed over the vegetation and smash into shrubs to immediately scramble groundward. Looking stunned, they find their burrows and squeeze through the entrance. An hour later, boomerang-winged, bluish-grey birds return to land and do the same — this time they are fairy and broad-billed prions. With all the aerial acrobatics there are casualties; some are hung by the neck, caught between forked branches. The two species of Chatham cave weta have evolved to help clean up these carcasses; they eat both vegetation and flesh. Dusk also brings returning little blue penguins waddling in from the waves and hopping up rocks, along wellworn paths to their burrows. And the cacophony begins — to continue all night, until the first rays of light — shrieking, squawking, even laughing, at extremely high volumes. Murderous danger lurks before dawn though, because the island’s top predator, the fearless brown skua, is hunting. Brown skua are built like very large black-backed gulls and sport a similar vocabulary. Morning brings dismembered evidence of last night’s kills around their nesting sites: feathers, strewn wings, eaten-out chest cavities — usually a prion. Dawn is welcomed by a mass exodus of tens of thousands of birds leaving for a day of ocean feeding. But did they really get any sleep?