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Chatham Island, east of New Zealand

The Chatham Islands are a small group of subantarctic islands with a unique and astonishingly rich biological heritage: the island group is home to 20 percent of New Zealand’s threatened bird species, and 14 percent of its threatened plants (NZDOC undated a). Located 800 km east of the South Island, this remote archipelago was one of the last places in the Pacific to be visited by humans. However, human settlement has taken a drastic toll on native biota. Alien species and large-scale land clearing devastated both vegetation and the native avifauna. Recent years have seen significant conservation work to restore native ecosystems and some dramatic success stories, such as the recovery of the Chatham Island black robin (Petroica traversi), which had dwindled to only one breeding pair by 1980 (Molloy 1994).

  • Scientific Code
    (AA0401)
  • Ecoregion Category
    Australasia
  • Size
    300 square miles
  • Status
    Critical/Endangered
  • Habitats

Description
Location and General Description
Located 800 km east of Christchurch, New Zealand (43° S, 176° W), this archipelago consists of two inhabited islands, Chatham and Pitt Islands, and approximately 40 islets and rock stacks. The archipelago was formed by volcanic upthrust almost 80 million years ago, and the islands are a mix of volcanic rocks, schists, and limestone. Like most oceanic islands, the Chatham Islands do not experience great temperature extremes, but the archipelago is subject to long periods of rain and high winds. The wet conditions, geologic and topographical diversity, and fertile soils of the Chatham Islands have all contributed to the development of a distinctive and diverse floral community.

Prior to human settlement, more than 90 percent of the archipelago was covered with a mosaic of forest, scrub, and swamp or heath. The Chatham forest flora has affinities with the Kermadec islands, Norfolk Island, and the New Zealand mainland, while the Chathams heathland has strong affinities with the flora of other subantarctic islands such as Campbell Island, the Snares and the Solander Islands. In these areas, endemic plants such as the Chatham Islands forget-me-not (Myosotidium hortensia), an endemic flax (Phormium spp.), rautini (Brachyglottis huntii), Chatham Islands kakaha (Astelia chathamica), and soft speargrass (Aciphylla dieffenbachii) can be found (NZDOC undated c). In the forests, tree ferns predominate, and their trunks provide rich germination sites for seedlings of other forest trees, filmy ferns and orchids. Nikau palms (Rhopalostylis sapida) are prominent in gullies. The long isolation of the Chatham Islands is reflected in the absence of beeches (Nothofagus) and podocarps.

Biodiversity Features
The Chatham Islands support 338 native land plants, 47 of which are endemic to the island group. Endemic plant species have adapted to the cool, wet and windy climate in a variety of ways. For example, the tarahinau (Dracophyllum arboreum) has wind-resistant needle leaves, the tree-daisies have protectively furred leaves and twigs, and megaherbs such as the Chatham Islands forget-me-not and giant sowthistle (Embergeria grandifolia) have giant leaves. Gigantism is common and examples include: Chatham Islands karamu (Coprosma chathamica) and the tree koromiko (Hebe barkeri), both of which are the largest species in their genera; and the akeake (Olearia traversii), one of the largest tree daisies on earth (NZDOC undated c).

The avifauna of the Chatham Islands is unique and varied. Millions of seabirds roost and breed in the Chatham Islands and their guano has helped create the fertile soils now found on the islands. Of particular interest is the taiko (Pterodroma magentae), a species that was known only from a single specimen collected in 1867. The taiko was rediscovered breeding in dense forests on Chatham Island in 1978 (Crockett 1994). The current population is estimated at approximately 150 individuals and is being actively protected by the New Zealand Department of Conservation. The Chatham Islands host a variety of wetland species as well, including ducks, swans, stilts, shags, and migratory waders. Bird life was even more prolific before the first Polynesians (Moriori) arrived approximately 700 years ago. Fossils show that over 20 petrel species lived here, but 8 species went extinct after the arrival of the Moriori (Molloy 1994). In total, 29 of the 67 total bird species and subspecies recorded here were extinct by European arrival, and another 8 were extirpated after European arrival (Stattersfield et al. 1998).

The following species and subspecies were eliminated after European settlement: the Chatham Island bellbird (Anthornis melanura melanocephala), Chatham Island fernbird (Megalurus rufescens), Diffenbach’s rail (Gallirallus dieffenbachii), Chatham Island rail (Gallirallus modestus), brown teal (Anas aucklandica), bittern (Botaurus poiciloptilus), New Zealand falcon (Falco novaeseelandiae), and New Zealand shoveler (Anas rhynchotis variegata) (Stattersfield et al. 1998, Heather and Robinson 1997). Seven endemic species or subspecis of landbird still survive in the islands: Chatham Island tui (Prosthemadera novaeseelandiae chathamensis), Chatham Island pigeon (Hemiphaga novaeseelandiae chathamensis), Chatham Island warbler (Gerygone albofrontata), Forbes' parakeet (Cyanoramphus auriceps forbesi), Chatham Island snipe (Coenocorypha aucklandica), Chatham Island tomtit (Petroica macrocephala chathamensis), and the Chatham Island black robin. All of these endemics are rare and recovery programs are underway for many of them. Globally threatened endemic seabirds include the Chatham Island oystercatcher (Haematopus chathamensis VU), Chatham Island snipe (Coenocorypha pusilla VU), Chatham Island petrel (Pterodroma axillaris CR) (Hilton-Taylor 2000).

Of the 750 to 800 insects described from the Chatham Islands, about twenty percent are endemic species (NZDOC undated b). Habitat destruction and introduced mammals have led to the loss of many species and the decimation of even more. Most endemics survive only on island refuges such as Mangere and Rangatira, although a few still survive in forest reserves on the main islands. It is worth noting that there are no native mammals, frogs, or geckos, although there is one subspecies of native skink, Leiolopisma nigriplantare nigriplantare.

Current Status
These islands were some of the last in the Pacific to be settled. A mixture of Moriori, Maori, and European settlers gave rise to the approximately 800 residents that remain on Chatham and Pitt Islands today (NZDOC a). Human settlement led to destructive practices such as large-scale vegetation clearing for farming and development in addition to the introduction of alien species. Pigs, wild cattle, horses, goats, Australian brush-tailed possums (Trichosurus vulpecula), as well as smaller animals, such as rats and mice have all been harmful to the native biota of the Chatham Islands. As a result native flora and fauna have largely been depleted. The New Zealand Department of Conservation manages 7 percent of the Chathams archipelago, coordinating a network of at least 40 publicly and privately owned reserves, including several fenced reserves on Chatham Island, where native tarahinau forests are now successfully regenerating.

Perhaps the most important conservation areas in the archipelago are Mangere and Rangatira Islands. Both of these government-owned islands are kept free of all introduced predators and pests, and visitor access is strictly controlled. Mangere Island now supports a remnant patch of akeake forest and healthy tundra communities of shrub daisies, iceplant (Disphyma spp.), koromiko, and megaherbs such as giant sowthistle and soft speargrass. The regenerating habitats on Mangere provide refuge for the endangered Chatham Island black robin, Chatham Islands snipe, and the Forbes parakeet. Seabirds are returning to the island, and petrel and shearwater burrows are common. Rangatira Island, like Mangere Island, was once almost completely cleared for farming, but native forests on the island have shown a remarkable recovery in the last 40 years.

The Chatham Islands ribbonwood (Plagianthus divaricatus), mahoe (Melicytus ramiflorus), akeake, and flax have all flourished since domestic stock were removed from the island. Endangered invertebrate species such as the Rangatira spider, Chathams giant click beetle (Amychus spp.), Pitt Island longhorn (Xyloteles costatus) and giant stick insect can be found here, and the native skink is abundant. Millions of seabirds use the island, including storm petrels (Oceantidae), sooty shearwaters (Puffinus griseus), broad-billed prions (Pachyptila vittata), and the critically endangered Chatham petrel which breeds only on Rangatira (NZDOC undated b). Rangatira is most famous for its role in the recovery of the Chatham Islands black robin. This species almost went extinct due to habitat destruction and predation by introduced mammals in the 1970s, and by 1981 the population had been reduced to 5 individuals (Merton 1990). The robins were transferred to Rangatira, and an intensive management program run by the Department of Conservation succeeded in boosting the population dramatically. Black robins have now been reintroduced to Mangere Island from Rangatira.

Types and Severity of Threats
Despite the recent success stories from the Chatham Islands, many species and habitats remain in a critical state. Human activities such as land clearing, trampling and grazing by domestic stock, and the spread of exotic species are all threats. Climate change may be threatening an endemic subspecies of albatross, Diomedea cauta eremita (Stattersfield et al. 1998). Peat extraction for fuel oil and wax is feasible on the peat-rich Chatham Islands, although current market prices mean it would not be very profitable (Given 1995). Chatham Island species are extremely vulnerable to extinction due to their restricted ranges and small populations. The introduction of exotic species has devastated native habitats and continue to threaten native species. Feral cattle, sheep, pigs and possums need to be controlled in order to prevent further damage to native vegetation, and predator control programs need to be continued to keep rats, mice, hedgehogs, cats, dogs, and wekas (Gallirallus spp.) in check. Introduced weeds such as gorse (Ulex europaeus), Chilean guava (Ugni molinae), and marram grass (Ammophila arenaria) are all problematic as well (Given 1995). If the Department of Conservation and local landowners continue to work together, the Chatham Islands flora and fauna should continue to recover from the first impacts of human settlement. A recent renaissance in Moriori culture has inspired interest in traditional systems of natural resource management (Molloy 1994).

Justification of Ecoregion Delineation
The Chatham Island Temperate Forest ecoregion corresponds completely with ‘Chatham Islands’ Centre of Plant Diversity (Given 1995) and ‘Chatham Islands’ Endemic Bird Area (Stattersfield et al. 1998).

References
Crockett, D.E. 1994. Rediscovery of Chatham Island taiko Pterodroma magentae. Notornis (Suppl.) 41: 49-60.

Given, D. 1995. Pages 513 – 515 in S.D. Davis, V.H. Heywood and A.C. Hamilton. editors. Centres of Plant Diversity. Volume 2. Asia, Australasia, and the Pacific. WWF/IUCN, IUCN Publications Unit, Cambridge, UK.

Heather, B.D. and H.A. Robertson. 1997. The field guide to the birds of New Zealand. Oxford University Press, Oxford, UK.

Hilton-Taylor, C. 2000. 1998. The IUCN 2000 Red List of Threatened Species. IUCN, Gland, Switzerland and Cambridge, United Kingdom.

Merton, D. 1990. The Chatham Island Black Robin. Forest and bird 21(3): 14-19.

Molloy, L. 1994. Wild New Zealand. New Zealand Department of Conservation/MIT Press, Cambridge, Massachusetts

New Zealand Department of Conservation (NZDOC). undated a. Chatham Islands: at a glance. http://www.doc.govt.nz/local/chathams/chathams01.htm. viewed August 28, 2001

NZDOC. undated b. Chatham Islands: animals. http://www.doc.govt.nz/local/chathams/chathams02.htm. viewed August 28, 2001

NZDOC. undated c. Chatham Islands: plants. http://www.doc.govt.nz/local/chathams/chathams09.htm. viewed August 28, 2001

Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wedge. 1998. Endemic bird areas of the World. Priorities for biodiversity conservation. BirdLife Conservation Series No. 7. BirdLife International, Cambridge, United Kingdom.

Tennyson, A. J. D. and P. R. Miller. 1994. Bird extinctions and fossil bones from Mangere Island, Chatham Islands. Notornis (Suppl.) 41: 165-178.

Prepared by: Winnie Roberts
Reviewed by:

 

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