Issue 3, September 2001
A Biodiversity Success Story on Tiritiri Matangi Island, New Zealand
Mechanical Engineering, Princeton University
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.
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
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.
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
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
Images courtesy of New Zealand's Department of Conservation.
New Zealand Department
of Conservation web pages at:
For related information also check http://www.enzed.com/wild.html
of Young Investigators. 2001. Volume Four.
Copyright © 2001 by Elizabeth Condliffe and JYI. All rights