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Issue 3, September 2001

A Biodiversity Success Story on Tiritiri Matangi Island, New Zealand

Elizabeth Condliffe
Mechanical Engineering, Princeton University
condliffe@jyi.org



blue takahes Five birds, including just one female, were all that remained of the black robin. The flightless, personality-rich, blue takahe was believed to be extinct. The only birds occasionally known to mate face-to-face, stitchbirds, were down to one isolated population. Saddlebacks were entirely isolated on a few islands and were put further at risk when predators introduced by a shipwreck killed their largest population.

Now visitors to Tiritiri Matangi Island see these birds regularly, thanks to the volunteer-driven conservation project that has been dubbed a "world success story".

Located just four kilometers from mainland New Zealand and only an hour's ferry ride from Auckland, Tiritiri Matangi Open Scientific Sanctuary is now home to many endangered, rare, and threatened species of native flora and birds. New Zealand sanctuaries are especially important because over 90% of the country's insects and marine molluscs, 80% of its trees, ferns, and flowering plants (including a sponge that produces a cancer-fighting substance), 25% of its bird species, and all of its reptiles are found nowhere else on Earth.

saddleback New Zealand‘s unique position derives from its creation and evolution without humans and most other mammals. In fact, the only mammal to inhabit New Zealand before humans arrived and introduced other species was a species of bat. Several birds, including the takahe, New Zealand's national icon, the kiwi, and the kakapo, the world's only flightless parrot, evolved without the use of their wings. The giant weta, a palm-sized insect, filled the niche of rodents in this unique ecosystem. Human habitation and the introduction of rodents, cattle, trees and other organisms have reduced the indigenous biodiversity on the island. Only the more resilient native species have remained.

Birds have been especially affected by the pests and foreign species brought by humans; a known 44 indigenous species are already extinct. Rats arrived at almost the same time as the early Maori settlers. Later, opossums were introduced to establish the New Zealand fur trade. Along with other mammals, these two species ate seeds, fruits, lizards, insects, eggs and even chicks, acting as both competitors for habitat and food as well as predators to New Zealand's indigenous species. Further loss of natural habitat occurred through the developing country along with the introduction of foreign weeds and trees. Tiritiri Matangi, itself, was cleared by successive farms before becoming a Hauraki Gulf Maritime Park in 1971.

Islands offer hope through their relatively easy eradication of pest, predators and weeds. In 1984, an effort began to re-vegetate its 220 hectares (90 acres) with native flora. This included removal of farm animals and plants, and planting over 280,000 trees. Careful planning ensured that the Pohutukawa - otherwise known as the New Zealand Christmas tree because of the large sprawling crown that blooms with red flowers in late December - were introduced early. Their protective canopy created suitable habitat for other native trees that would otherwise struggle to compete with the thick grasses and exposed conditions. (Incidentally, the name Tiritiri Matangi means ‘looking to the wind' or ‘wind tossing about'.) In 1993, the Department of Conservation removed the only introduced rodent, Pacific rats, thus permitting a "carpet of regenerating seedlings" to grow untroubled by exotic predators. As the natural habitat returned, native birds were reintroduced.

kiwi bird Unlike similar projects on other off-shore islands, Tiritiri Matangi is an open sanctuary, which means that its over 20,000 annual visitors can now admire the results of efforts by the Department of Conservation, the Supporters of Tiritiri Matangi Inc., and volunteers. The project, however, is not complete. In March 2000, the New Zealand Parliament launched a New Zealand Biodiversity Strategy attempting to reclaim the country's indigenous biodiversity while still recognizing the value of the introduced sheep, pine trees and kiwi fruit. To that end, it allocated funding for maintenance and restoration of New Zealand's habitats, ecosystems, and populations of native species. With much of the habitat restored on Tiritiri Matangi, the focus now is on its maintenance toward a naturally-sustainable state and on actively attempting to breed more endangered species there.

With population numbers as low as they were in the case of the black robin, real genetic diversity is a pipe dream. All black robins now are descendants of that one female. Fortunately, after years of inbreeding, the population can now select mates outside of the immediate family.

A similar situation has occurred with the takahe. Although they used to be found on both the North Island and South Island, current takahes are all descendants of fewer than 130 birds found on the west coast of the South Island after the species was thought to be extinct. To prevent a single event from eliminating the species, a few breeding pairs were translocated to islands like Tiritiri Matangi. Over sixty birds now inhabit the offshore, rodent-free islands, proving that these birds not only thrive without the introduced competition, but also that they can readily adapt to a new home.

Tiritiri Matangi now has seven breeding pairs of takahe, one lone male and two juveniles. Its aviary has been used to house birds before translocations in an attempt to force island birds to pair with their now relatively distantly-related mainland cousins. These efforts are working to reduce the founder effect, which occurs when populations are started from a small number of pioneer individuals of an original population. Unfortunately for genetic diversity, the birds have reorganized themselves into more closely-related mating pairs. For each pair generally 1-3 eggs are laid, 80% of those hatch and only one chick survives the first winter. This past year, six chicks hatched on Tiritiri Matangi, but only two juveniles survived.

Similar infertility issues have arisen with other species as well. Although this might be attributed to inbreeding, researchers have been unable to prove that reduced genetic diversity is the primary cause. Regardless of the troubles, the surviving birds seem vibrant, and there are a growing number of success stories. With the help of the Tiritiri Matangi Sanctuary, saddlebacks have been removed from the endangered species list and are now classified as rare species. Proof of other success lies in the awe-inspiring volume of the dawn chorus.



Thanks to the Tiritiri Matangi Island Department of Conservation officers who provided the primary information used to write this article.

Images courtesy of New Zealand's Department of Conservation.


Suggested Reading

New Zealand Department of Conservation web pages at:
http://www.doc.govt.nz
http://www.doc.govt.nz/cons
http://www.doc.govt.nz/cons/native
http://www.doc.govt.nz/cons/bidiversity/speech_pm.html


For related information also check http://www.enzed.com/wild.html


Journal of Young Investigators. 2001. Volume Four.
Copyright © 2001 by Elizabeth Condliffe and JYI. All rights reserved.
 
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