ISLANDS Refuges for Threatened Species

Forest and Bird, Volume 21, Issue 3, 1 August 1990, Page 28

ISLANDS Refuges for Threatened Species

Salvation for many of New Zealand’s native species lies in the sanctuary of the offshore and outlying islands dotted around our shores. Dr John Craig reports on the successes and failures of island bird transfers and some of the issues involved.

WO HUNDRED AND FIFTY PEOPLE stood around four boxes and watched 40 small birds fly to freedom on a new island. As the birds left their travel boxes, the last was still eating — not yet realising that the door was open. The birds, oblivious to the people, eventually gathered in nearby trees, some calling to re-establish contact, others feeding immediately in their new home. This first release of whitehead onto Tiritiri Matangi Island was just another planned transfer of one of our endemic native birds to an offshore island. Over 150 such releases have been made during the last century although the reasons, methods, success and personnel involved have varied widely. Human colonization of New Zealand has had an enormous impact on our native fauna and flora. The extensive destruction of forest, wetlands, tussocklands and shrublands greatly reduced wildlife habitat and the plight of native birds has been compounded by the introduction of mammalian predators and herbivores. Eradication or even effective control of mammalian pests on the mainland is expensive and time consuming, and current control techniques are effective for only a short period. Island transfers are an essential safeguard against mainland extinctions. With over 700 islands around the coast we are fortunate to have a chance to retain some of our precious endangered wildlife.

Islands Important

The importance of islands for the long term conservation of our native animals was recognised at the end of the last century when a flurry of activity saw kakapo and kiwi released onto a number of islands. Government purchase of Hauturu (Little Barrier), Kapiti and Resolution Islands was an important part of this early conservation effort and Hauturu and Kapiti remain a prime part of our conservation estate. The mammoth efforts of Richard Henry on Resolution Island are known to most not for the success but for the total failure of his venture. For the conservation of most threatened species, islands are only useful if they do not have harmful introduced mammals and are far enough offshore to preclude invasion by stoats, rats and deer. It was ignorance of these very points which caused the failure of many early bird transfers to islands. For example, early transfers of kakapo and saddleback to Hauturu and Kapiti failed because both islands already had cats and Kapiti also had Norway rats. It was the subsequent arrival of stoats that spelt doom to the hundreds of kakapo and kiwi Richard Henry had transferred to Resolution Island. The late Gordon Williams, a director of the Wildlife Service, noted that the "salutary lesson (of choosing islands out of the swimming range of stoats) remains unforgotten and strongly influences the choice of receptor islands by Henry's successors’. The unfortunate use of Maud and Motukawanui Islands for saddleback transfers and their subsequent loss to stoats suggests that the reasons for Richard Henry's failure was still not fully appreciated. The continued use of Maud Island, known to be within the swimming range of stoats, for transfers of some of our rarest animals, such as kakapo, takahe and giant weta, highlights an ongoing dilemma for wildlife managers.

Success or Failure?

Why do some releases succeed and others fail? Largely we do not know, and it is unlikely that the same factors are responsible each time. Predators are clearly responsible in the examples of saddleback declines on Kapiti, Maud and Motukawanui. Catastrophes such as cyclones soon after release can reduce numbers to very low levels as well. For example, a cyclone killed most of the first Wildlife Service release of red-crowned kakariki on Tiritiri. Similarly a few days after a subsequent release done by Auckland University, a cyclone struck and we picked up many of the new birds dead on tracks. Competition from related species, another factor that influences the outcome of a transfer, can usually be avoided although it does present difficulties in the case of the stitchbird. There is a very marked dominance hierarchy among our three honeyeaters, and stitchbird (especially the females) are at the bottom of this pecking order. This means that establishing small numbers of stitchbirds on islands where bellbirds are already present in large numbers will be difficult. For this reason islands such as Mokoia, now that the rats have been removed and Rangitoto, once the cats, rats and stoats have been removed, may offer the best chance for future transfers of our rarest honeyeater. People often point to the small numbers of birds relocated as a reason for transfer failure but we have few releases of small numbers

that are not complicated by other variables such as predators. Anticipating problems with transfers of the few remaining black robin, Doug Flack released just five South Island robins onto Motuara and Alports Islands in the Marlborough Sounds. Both transfers were successful. The eventual transfer of the last seven black robins was also successful although it was the intensive management by Don Merton and his dedicated team that saved this species from extinction. These successful transfers of small numbers of robins contrasts with the inexplicable failure of two saddleback transfers of 29 (1968) and 30 (1985) to Fanal Island in the Far North. Overseas work has suggested that known pairs and neighbours often establish better than a random mix of individuals. In the 1984 saddleback transfer onto Tiritiri Island, groupings of known pairs from the same area on Cuvier and hence sharing the same song were released into the same forest patch together. Most of these pair bonds remained intact during the first year and the Tiritiri population had the highest survival rate of any saddleback release. A planned trial release of pairs and unpaired saddleback onto Kapiti by Tim Lovegrove appears to have produced the reverse result with many of the pairs separating. While many factors differed between these releases, we would clearly benefit by planning future translocations as scientific trials to test the influence of numbers and sociality.

Insignificant Failures

The few failures pale into insignificance compared with the enormous numbers of successful transfers. Although North Island saddlebacks failed on Fanal Island, transfers elsewhere have been so successful that we can hardly consider North Island saddleback endangered any longer. Saddleback provide an excellent example of how continued success and the development of transfer technology has allowed increasingly bold and innovative transfers, which continue to keep New Zealand at the forefront of bird transfer work. Between 1925 and 1950 several unsuccessful attempts were made to transfer North Island saddleback onto islands in addition to Hen. The real successes began in the 1960s when transfers were made to Whatupuke (1964), Red Mercury (1966) and then Cuvier (1968). The experience gained in the Whatupuke transfer proved invaluable when a rapid response was needed to the ship rat invasion of Big South Cape Islands. South Island saddleback were rapidly transferred to islands nearby and subsequently as far as the Marlborough Sounds. The continued success of saddleback transfers onto kiore-only islands but their failure to increase on Kapiti led to a highly innovative programme by Tim Lovegrove. Noticing that many saddleback were lost to Norway rats and weka at roost and nest sites, Tim began a programme of providing roost and nest boxes on Kapiti. By erecting similar boxes on Kawhitihu (Stanley) Island he established a trained source population. Even this mammoth task (involving many volunteers) has failed to produce a population that can increase in the presence of rats and hopes of eventual transfers to the mainland have faded. The prospect for Kapiti populations

looks brighter as increasing successes in rodent eradication on islands (kiore off Korupuke and Raurima, Norway rats off Whale and Breaksea and mice off Mana to mention just a few) suggest that Kapiti could be rid of rodents if funds are available.

New Technologies

Transfer technologies have increased markedly in recent years. The intensive trials of aviary holding, feeding and transfer methods requested prior to David Allen's whitehead transfer from Hauturu to Tiritiri and the provision of temporary aviaries, nest and roost boxes plus supplementary feeding for saddleback transferred to Kapiti are a vast improvement on the transfers of even the 1960s and early 1970s. Gordon Williams rightly called these and earlier attempts "marooning" as little other than selection of release sites was possible. Many early island releases were reactive attempts to save species from impending extinction but there is an increasing movement towards carefully planned transfers as part of integrated conservation management. With this change comes increasing scientific and public debate of the plethora of factors that must be considered when planning transfers. The Conference on the Ecological Restoration of Islands held in Auckland in December 1989 brought together many of the people involved in island management and research. Advantages and disadvantages of animal and plant transfers were considered and debated. The proceedings of this conference will provide important material for future planning and discussion. One issue is the impact of transfers on existing flora and fauna. With the exception of the transfer of one lizard, one insect, and two snail species, all recorded animal transfers for conservation in New Zealand have been of birds. The increasing awareness of New Zealanders that their highly distinctive native animals include more than birds has led to questions of whether all transfers have been beneficial. For example, many people consider the numerous transfers of weka to offshore islands as detrimental. Weka are implicated in the loss of little spotted kiwi eggs, saddleback fledglings on Kapiti and Cook's petrels on Codfish Island. They have been removed from Codfish Island in case they might harm kakapo and petrels. Most weka releases were originally to provide food for people on remote islands — conservation was not a consideration. However, the transfer of buff weka to the Chathams in 1905 has ensured the survival of that weka which subsequently disappeared from the South Island mainland. Recently Mike Meads and Alison Ballance have suggested that saddleback introduced onto Mercury Islands and Hauturu may adversely affected the tree and giant weta populations. We can avoid similar conflicts on Maud Island by continuing to fence takahe out of sensitive areas and ensuring that saddleback are not re-released. It is important to realise that other native species have preyed on birds — the loss of Antipodes Island kakariki to tuatara predation on Stephens Island is the most obvious example. Careful planning is the key. In the past, the least modified islands were considered the most desirable for transfers of endangered

species as these were the only places which seemed to have sufficient and suitable habitat. Our increased ability to remove noxious mammals means that we can now leave our more pristine islands untouched and select some of our highly modified islands for rehabilitation and transfers. Conflicts will still arise, however, as the example of Mana Island has shown. Use of rehabilitated islands has the added advantage of allowing involvement by the public. There is always a danger that releasing too many species onto an island will upset the existing community balance. Careful choice of species will minimise this risk and the greatest care should be taken with our least modified islands. During the last 30 years five bird species have been released on Maud Island and Hauturu, Kapiti and Tiritiri have received four species. Releases on Maud and Kapiti have met with mixed success, and it will be some time before we know the outcome of the kakapo and black petrel releases onto Hauturu. Both were laudable experiments, but given the results of transfers of shearwaters onto Bass Strait Islands we should not be too hopeful for the black petrel work.

Phenomenal Success

Tiritiri has been a phenomenal success. All four new species have bred in their first year, with two of them breeding at far higher rates than elsewhere. Brown teal have reared two broods instead of one each year, and saddlebacks have been producing up to four broods per season. Moreover, instead of producing the usual clutch of two, some birds have been laying three and four eggs. Approximately 100 young saddlebacks were fledged in the 1989/90 season; they have been astonishingly productive! Most past island transfers have been for the protection of threatened species. This has involved no public debate and has totally excluded public involvement both during and after the transfer. There is an increasing realization that conservation is for people of both present and future generations and we can all benefit greatly by establishing wild populations of rare birds on islands accessible to the public. Tiritiri Matangi Island is the best example of this approach. Similar projects on Mana Island and Motuora (Hauraki Gulf) are planned. The development of Tiritiri was planned to provide an open sanctuary for rare animals. Since 1984 over 180,000 trees have been planted by thousands of volunteers. These trees have grown so rapidly that birds includ-

ing saddleback already live and breed in the regenerating forest. Releases have included red-crowned kakariki (4), saddleback, brown teal, whitehead (2) and in the near future will include more brown teal, plus robin, takahe and little-spotted kiwi. From a little-visited island of the 1970s (200-300 people per year), visitor numbers are growing rapidly with over 8,000 expected in 1990. Visits to witness bird releases are most popular. Involving the public in conservation is important from the early planning phase. Many people do not see why indigenous species, especially birds, should receive so much attention as all animals including exotic species have the right to exist. When Neil Mitchell and I suggested in 1982 that wallaby and possum should be removed from Rangitoto and Motutapu the response of some people was to release wallaby on Brown's and Great Barrier Island. Similarly when it was announced that weka would not be released on Tiritiri as they may compromise other transfers, someone put a weka on the island. These actions demonstrate that the public do have views, some strongly held, and it is important to allow full and open debate to ensure that plans include as many viewpoints as possible. I believe that present plans to remove wallaby and possum from Rangitoto and Motutapu will receive wider support if rodents, cats and mustelids are removed at the same time. Everyone should be informed that the value of these islands will be greatly enhanced by removing exotic animals to allow transfers of rare native birds such as stitchbird, saddleback, kakariki and whitehead. The public readily associate with birds so let us use them to ensure the best for both the plants and the animals! Most of the previous transfers were initiated and carried out by staff of the Department of Conservation or its predecessor, the Wildlife Service. Names such as Brian Bell, Don Merton and Dick Veitch crop up time and time again. More recently private individuals, including Forest and Bird groups, have initiated island and mainland transfers. Bellbird, robin and brown teal transfers to Moturoa Island, and bellbirds to Waiheke and to Whangarei Heads are examples. Island transfers of birds, which have been responsible for saving many species such as black robin and saddlebacks, have readily captured public attention. They take conservation into everyone's living room via the media, and as seen on Tiritiri Matangi are actively involving New Zealanders. As such, bird transfers are powerful weapons to counter public apathy and can with sponsorship be used to bolster New Zealand's small budget for conservation. Finally, bird transfers and associated pest eradications are responsible for an important part of New Zealand’s international image in conservation. ¥ John L. Craig is an Associate Professor in Zoology and Deputy Dean of Science at Auckland University. He teaches behaviour, ecology and conservation and is a keen advocate for more public participation and debate in conservation. His own and his graduate student research is largely on native birds and introduced mammals, especially fantail, pukeko, bellbird, tui, saddleback and kiore. He has been actively involved in the Tiritiri ‘open sanctuary’. John considers himself fortunate to have been involved in three releases of red-crowned kakariki, two of brown teal, three of bellbird, plus one each of saddleback, kakapo and whitehead.