Story: Threatened species

Page 4. Case histories

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Mahoenui giant wētā

Wētā are insects unique to New Zealand. Related to crickets and grasshoppers, they have remained relatively unchanged over millions of years. There are around 100 species, including the giant wētā.

The Mahoenui giant wētā (Deinacrida mahoenui) is a ‘nationally endangered’ species discovered in 1962 in a patch of spiny gorse at Mahoenui in the North Island’s King Country. The gorse may have protected it from rats, and therefore extinction. Since the late 1980s, there have been attempts to start new populations elsewhere. Hopes centred on islands off the Coromandel coast, but by 2007 the only success was in another gorse-ridden patch near Te Kūiti.

In 2000, 124 wētā were released into the gorse patch, and another 60 in 2001. A follow-up survey found insects that were all under a year old – offspring of the transferred wētā. In 2003 the Department of Conservation noted that although there were thousands of wētā, they were on just one paddock and therefore vulnerable to fire, which would spell tragedy for the species.

Mistletoe

Like the canaries sent into a coal mine to test for dangerous gases, New Zealand’s showy Peraxilla mistletoes are key indicators of the health of the forest. As mistletoe depends on birds, lizards and insects for pollination, good numbers of it suggest a sizeable population of native animals, and an absence of plant-eating browsers such as possums.

The mistletoe flower remains closed until a bird, lizard or insect twists the top, at which point it bursts open. These plants are among the few in the world that are ‘explosive’ pollinators.

Two species of the scarlet Peraxilla mistletoes attach themselves to beech trees – P. colensoi and P. tetrapetala. These are considered to be in ‘gradual decline’. Possums eat them, and predators have reduced the native birds and insects that pollinate them.

Five that survive

The Codfish Island fernbird, Campbell Island mollymawk, crested grebe, black petrel, and a snail of the Chatham Islands are five of New Zealand’s native species whose conservation status improved in 2005.

Conservation groups are working to maintain mistletoes by trapping rats and possums, and planting host trees for these beautiful plants.

Tuatara

New Zealand’s tuatara (Sphenodon punctatus) is a species of ancient, lizard-like reptile. There are reasonably good numbers on the stronghold of Stephens Island, in Cook Strait. Its ‘range restricted’ conservation rating reflects the fact it occurs on only a few islands, even though there may be up to 100,000 individuals.

The tuatara has been moved to islands from the Coromandel northwards. After kiore (Pacific rats) were finally wiped out on Little Barrier Island (Hauturu) in 2004, progeny of tuatara originally rescued from that island were returned. As Little Barrier is six times larger than the next biggest tuatara island (Hen Island), there is huge potential for re-establishing the species.

The Brothers islands tuatara

It was not until the late 1980s that the tuatara Sphenodon guntheri, which had somehow survived on a tiny island of The Brothers group in Cook Strait, was described as a separate species. They are considered ‘nationally endangered’ because in 2005 there were fewer than 1,000.

Scientists at Victoria University of Wellington began a captive rearing programme, and in 1995 released the first juveniles onto Tītī Island in the Marlborough Sounds. A second group was moved to Matiu (Somes Island) in Wellington Harbour in 1998.

How to cite this page:

Gerard Hutching and Carl Walrond, 'Threatened species - Case histories', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/threatened-species/page-4 (accessed 12 November 2019)

Story by Gerard Hutching and Carl Walrond, published 24 Sep 2007