It was the clatter of retired professor Euan Young preparing porridge that woke us. In the tiny Department of Conservation cabin that was home to four of us on Mangere Island in the Chathams, there was little space for privacy. Yesterday a fishing boat had dropped us on this remote 113 ha wildlife sanctuary to pursue a bevy of scientific projects. Now it was time for work.
Young, a bird specialist and regular visitor to the island, headed off with his skua gear and a gigantic sweep-net. After a ten-minute walk uphill he reached his first customers, a skua family with two chicks. The moment he crossed some invisible border in the vicinity of the nest, the adult birds launched a furious attack. One dive followed another, with beak and claw slicing past Young’s head.
The professor was undeterred; this was his chance to make a capture. One dextrous swing of the net and a skua was struggling angrily in the mesh. Leg bands that he had applied in previous years allowed him to identify the bird. Once he had caught the second skua, he knew that this was the oldest pair on the Chathams. They had been together 19 years—longer than many married humans. Two chicks, still incapable of flight, were quickly apprehended in the high grass. They, too, received bands, and yielded a small blood sample.
Genetic analysis of blood can show which bird has fathered which offspring as big a boon to ornithologists as to human paternity investigators. This sophisticated technique, together with painstaking field observations, has given uncommon insight into the social life of skuas. Although some families consist of a female, a male and one or two chicks, there are also numerous “families” which consist of one female and up to five males. Two chicks in such a family may well have different fathers, yet often surplus males do not father any chicks at all, and it is unclear what biological advantage they derive from the arrangement.
Young managed to catch, band and take blood samples from 10 birds that morning. In doing so he covered most of the accessible part of Mangere Island.
In pre-European times movement would not have been so easy. Lush, dark-green bush stretched over almost the entire island. Only small areas with very shallow soils and frequent landslides would have been covered by the herbs and shrubs which are now a feature of the island. Scrambling among massive old trees would have brought encounters with black robins, Forbes’ parakeets, the unique Mangere rail and the Chatham Island bellbird. With every second footstep the visitor would have subsided into a 50 cm-deep hole, the work of burrowing seabirds such as broad-billed prions, fairy prions, common diving petrels and sooty shearwaters—all of which are described as “mining seabirds.”
Today, only a fragment of the original diversity of bird life remains. The Mangere rail and the Chatham Island bellbird are extinct. The common diving petrel can no longer be found on Mangere Island, while the black robin and Forbes’ parakeet are endangered. Only the broad-billed prion, fairy prion, and sooty shearwater are still present in good numbers.
Between the arrival of the Moriori and the early 19th century, 18 bird species were wiped out on the Chatham Islands. How many of these were present on Mangere Island is not clear. What is known is that 11 bird species were lost from Mangere after European settlement of the Chathams in about 1830 as a result of repeated burnings of the bush and the introduction of sheep and rabbits. No people actually lived here.The rabbits soon became a nuisance, so cats were introduced to control them around 1890.
In short order, Mangere Island was left almost bare of trees, and a large number of native animals were wiped out or driven close to extinction. All that remained of the original forest was a tiny 3 ha remnant at the foot of the highest cliff, and scattered old trees which, deprived of the shelter of the bush around them, had to struggle to withstand the frequent storms. These storms have now battered the trees into absurd shapes, with branches remaining only on the downwind side of their trunks.
The island’s wildlife situation started to improve only in the 1950s after cats disappeared—they had long since eliminated the rabbits. In 1966, the island was purchased by the Crown, and two years later the last of the 800-900 sheep were removed.
The ongoing restoration and recovery of Mangere Island has been a painfully slow process. In 1973, the Wildlife Service tried for the first time to plant new trees, but the island’s steepness and remoteness made it extraordinarily difficult to land plants from the sea. Between 1975 and 1979, more than 100,000 akeake trees (Olearia traversii) were airdropped on to the island. Several thousand missed the island completely and were lost at sea.
Most of these trees had been grown in New Zealand from cuttings clipped off hedgerows in Dunedin—a type of genetic mixing no longer favoured in forest restoration work. In the late 1970s roughly 10,000 flax bushes were planted to provide shelter for young trees. In the following years, some ngaio (Myoporum laetum), karaka (Cotynocarpus laevigatus), and Hebe dieffenbacbii were planted to give greater diversity.
Most of the trees planted on Mangere Island this decade have been grown from local seed by Chatham Island and Pitt Island people, who also do most of the planting. The most successful species is akeake, which grows much faster than any other plant and seems better able to compete with the dense sward of introduced grasses. It is hoped to eventually plant up to 50 per cent of Mangere Island in trees. Once akeake grows up and shades out the grass, birds will spread the seed of other species, but it will be several generations before forest is once more thick over the island.
Euan kennedy, an officer with DoC, spent much of his morning attending to domestic tasks surprisingly time-consuming in the absence of appliances such as washing machines. No fridge on Mangere Island means that meat can’t be stored, and fishing is an almost daily task.
After lunch, Kennedy took the island’s only track to Robin Bush to survey the famous black robins, a species which numbered only five individuals in 1979. Most birds flee human intruders, but the robins are now habituated to people. They know that the presence of humans means an easy meal, because they get rewarded with meal worms for putting in an appearance. Over the years of intensive work to save the black robins from extinction, the robins and their minders have developed this mutually beneficial behaviour: the birds are supplied with valuable food, and the humans more readily find the robins in the dark bush.
These days, black robins need little outside help, but a close eye is still kept on the total population of 150 birds which are living on two islands: Mangere, home to around 40 robins, and South East Island, 15 kilometres away, with the remainder. Interestingly, there are differences between these two populations. The birds on Mangere Island breed a little earlier in the season, produce more offspring and live at a higher density. No one knows why these differences occur.
For years the robin team was satisfied with the progress of the vulnerable species, and the biggest threat was thought to be rats or cats reaching one of these predator-free islands. But two seasons ago a new and unexpected danger loomed on Mangere Island. A male robin fancied a female tomtit, and their clutch proved to be fertile. Two chicks hatched, and one of these hybrids grew to maturity. If robins and tomtits were to regularly interbreed and form a hybrid population, it could signal the end of the black robin as a separate species. So far, no further examples of this union have arisen, but the robin team is vigilant.
While Kennedy checked a robin nest for chicks, a representative of another bird species also near extinction emerged from the shadows on the forest floor. It was a Chatham Island snipe, a species which author Michael King described in his book on the Chathams, A Land Apart, as “mortally unafraid of predators.”
A fist-sized wading bird, the snipe spends most of its time poking a long beak into the leaf litter, searching for insects and worms, and gives little heed to people. It is one of the species that was eliminated when cats roamed Mangere Island, but was successfully reintroduced in 1970. Since then, snipe have flourished and spread to Pitt Island and the Star Keys, 15 km east of Pitt. With at least four islands now inhabited by the bird, two of which support reasonably large populations (Mangere and South East Island), its future seems assured.
Around the DoC hut, Forbes’ parakeets sip nectar from the flowering introduced flax plants—a valuable addition to their diet of leaves, flowers and seeds. Only while flying do the parakeets reveal their true beauty. Their flight is swift and elegant, and beneath their uplifted wings metallic blue flashes contrast with the red, yellow and vivid green of the rest of the bird to impart a spectacular and exotic appearance. Forbes’ parakeet is a subspecies of the yellow crowned parakeet of mainland New Zealand. Only Mangere Island and neighbouring Little Mangere are home to the subspecies.
While the two Euans were busy with their bird catching, German PhD student Katrin Schops was sc. L – ting out on the thankless task of lo cating and mapping every speargrass plant on the island—strenuous work, given that the island’s steep slopes are covered with thick mats of grass that are often more than knee deep.
Dieffenbach’s speargrass, an endangered species, has actually benefited from the burning of the island. Once restricted to the steep cliffs and other open areas, it is now patchily distributed over most of the island. A relative of the carrot, the species can grow to over a metre in diameter and a height of up to 60 cm. The leaves have a feathery shape and, unlike other speargrass species, are relatively soft and lack spines. In early summer the attractive yellow flowers of look like large feather dusters, bathing the slopes in a lemon glow.
Schops’ interest in these plants stems from the fact that they are the only food source of a large endangered weevil that lives only on Mangere and South East Island. Her studies have made her known locally as the “weevil-woman.”
At 8 pm. we gathered around the radio for the daily “sked” with the DoC base on Chatham Island—a safety precaution to make sure everybody is all right and that things are running according to plan. These rendezvous by radio are our only contact with the outside world. Work details are exchanged, and sometimes we get cricket or rugby results and other important news.
As darkness fell, the twilight air suddenly swirled with birds, and the ground came alive with weta. Little blue penguins clambered uphill, pausing to preen or socialise as they climbed. The place was unrecognisable from the Mangere Island of daytime. Thousands and thousands of seabirds—broad-billed prions, fairy prions, grey-backed stormy petrels and sooty shearwaters—wheeled in from the sea where they had spent the day feeding. In the gathering dusk they flew to their nest burrows to relieve their incubating partner or to feed the chicks.
On the far-stretching horizon, flocks of birds suddenly became visible as they homed in on the island. Individuals became larger and larger until they landed clumsily on the ground, and a few moments later vanished beneath it. During the day the island had seemed relatively uninhabited; now it was Heathrow airport! It is estimated that hundreds of thousands of seabirds nest on Mangere Island, and each day they all come ashore in the space of a few hours.
For these birds, the arrival on Mangere Island is the most dangerous part of their daily routine. A cordon of 30-50 skuas is in the air to hunt the incoming birds. It is a gauntlet of death. The robust skuas attack in the air, forcing their prey on to the ground. They kill and swallow the smaller birds on the spot, and pluck and feed from the bigger ones. The island’s abundant weta profit from these meals, as they scavenge the remains of the birds.
But the weta themselves are prey for one of the biggest spiders in New Zealand. Dolomedes schauinslandi, which grows to the size of a man’s palm, hides under plants and in crevices during the day, but at night comes out and hunts for insects. Normally these impressive arthropods are not very conspicuous, but in late summer the females sit exposed on their webs, spun over twigs and lumps of grass, guarding their eggs. Here they become very aggressive. They’ll even attack a hand they perceive as threatening.
Back in the hut, Schops was getting ready for a night out “weeviling.” Weevils are a type of beetle, with a large elongated snout. The most well known are small store pests such as maize and granary weevils, but only a small number of weevil species feed on human food. The rest can be found in almost any habitat, many of them so specialised that they feed on only a single plant species.
The Dieffenbach’s speargrass weevil which Schops studies is entirely nocturnal. As its name suggests, it is a specialist feeder on this one species of speargrass. During the day the large, flightless insects hide in dense vegetation, but at dusk they come out of their hiding places. Like stiff old robots, they walk slowly up the leaves and flower stalks of their food plants. While marching upwards they often pause—as though in need of winding up—but after a moment continue at the same sedate pace until they reach a suitable spot for feeding.
Before Schops started her study in 1993, it was assumed that this weevil was a rare species restricted to Mangere Island, with a few on South East Island—although it had once been widely distributed over the Chathams. Part of her task has been to estimate the number of beetles on Mangere Island. To do this, she has to identify weevils individually—no easy task when dealing with thousands of very similar-looking insects. She has adopted a technique used by European beekeepers, who glue numbered plastic tags on to their queen bees in order to distinguish between them.
The night was warm and humid, and hundreds of weevils were feeding on the leaves and stems of the speargrass plants. I helped Schops collect and store specimens in plastic containers. After a few hours of intensive searching, we carried the harvest carefully back to the hut.
In the morning a numbered plastic tag would be glued to the back of each weevil, and the insects returned to the plants from which they had been collected. Schops estimates that Mangere has about 12,000 speargrass weevils. Although this sounds like a large population, it is still rather small for an insect species living in a few speargrass patches amidst a sea of grass that could very easily catch fire . To ensure that this unique and peculiar insect survives, it will probably be necessary to enlarge the small weevil population on South East Island or to establish another population on one of the other islands of the Chatham group.At 2.30 A.M. we crawled into our sleeping bags, finished for the day.
In a few hours the eastern sky would start to brighten, and the prions and petrels fly out to sea again. The weevils and spiders would go into hiding, and the island’s three remaining pairs of Chatham Island pied oystercatcher start their first squabbles of the day.Another day in the life of a special island ark has begun.