Mokoia Island

Restoration Programme

History | Mammal Eradication | Translocations & Research | Public Involvement | The Future | References

Mokoia is a 135 ha island in lake Rotorua, in the central part of the North Island. The summit is 150 m above lake level, and the shortest distance from the mainland is about 2.1km. Mokoia has had a long history of human habitation, and is highly modified. Mokoia has been revegetating naturally for about 40 years, and now has well developed secondary growth. Recent restoration efforts have involved mammal eradications, bird translocations, and a recent translocation of two mistletoe species.

Two images of Mokoia Island, contrasting the scrubby vegetation found at the summit, and the closed canopy forest found in D Gully.


Mokoia has fertile soil, and was used by Te Arawa for cultivation of crops (especially Kumara) for hundreds of years (Andrews 1992). Most of the bush was cleared and fired, and the steep slopes of the island cut into terraces. Many native trees were also planted on the island, including karaka, totara, whau, and puriri. European missionaries began visiting in the early 1800s, resulting in a wide variety of other crops and trees being planted. The only remnants of this planting are some poplars and few fruit trees. The most important European impact was the accidental introduction of Norway rats, which were already abundant by 1840. Mice also established, but it's unclear when they did so. Cattle, sheep, horses, pigs, and cats were deliberately brought to Mokoia. Like Tiri, Mokoia never had possums or mustelids.

Mokoia has had a long history of conflict, mostly among local hapu, but also including an invasion by Nga Puhi in 1823. The conflict moved to the courts this century, with a series of land court hearings from 1916 to 1955. Mokoia was subject to claims from many hapu, but was ultimately legally awarded to four hapu: Ngati Whakaue, Ngati Uenukukopako, Ngati Rangiwewehi, and Ngati Rangiteaorere. Mokoia is now administered by a trust board made up of representatives of these hapu. Mokoia is also classified as a Wildlife Refuge under the Wildlife Act (1953).

Cultivation on Mokoia had largely stopped by 1950. In 1952, the Department of Internal Affairs obtained a 6-year lease to farm pheasants on Mokoia. Mokoia was used as a safe haven for young pheasants, which were later released elsewhere for hunting. That project ended in 1956, and its main effect on the island was probably a population explosion of rats due to the grain used to feed the pheasants. Weka were also transferred to Mokoia sometime in the 1950's. The birds released were surplus birds from a transfer from Gisborne to Coromandel, and were re-routed by a local conservator of wildlife.

The cleared areas of Mokoia were initially colonised by bracken, but most of the bracken has now been succeeded by secondary scrub and forest. There is a mosaic of vegetation types, reflecting the recent history of disturbance. The majority of the island is scrub/forest dominated by mahoe, puahau (five finger), kohuhu, rangiora, hangehange, and kawakawa. The oldest forest is dominated by mamaku, kohekohe, mahoe, and karaka. Most of the younger areas are still in bracken and other fern, but the most recently clear portion of the island -- the eastern flat -- has mostly been taken over by blackberry.

The first restoration efforts began in the late 1960s, when thousands of tree seedlings and ferns were planted. However, rats were extremely abundant at the time, and probably destroyed most of the seedlings. These plantings seem to have had negligible effect on the vegetation. Goats were released onto the eastern flat in 1985 to control the blackberry, but managed to escape through the electric fence that was supposed to keep them out of the bush. By 1989, the scrub/forest understorey was very open, with no further regeneration taking place. This was presumably due to goat browsing, but the rats may have helped and there were also some sheep still running wild at that time.

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Mammal Eradication

Rats, goats, and sheep were eradicated from Mokoia in 1989-90. The rat eradication was organised by Paul Jansen (DoC, Bay of Plenty), and was conducted mostly by Conservation Corp workers. The island was gridded at 50m intervals, and 800 plastic bait tunnels put out with brodifacoum (Talon 50 wb) cereal pellets . These were checked and re-baited for 3 months, after which there was no further bait intake. Goats and sheep were shot as they were encountered. No further goats or sheep were ever seen. No rats were seen until late 1995, by which time they had re-colonised in low numbers.

Mice were also presumably killed by the poison. However, their numbers seemed to increase after the poisoning, perhaps due to lack of competition and/or predation from rats. Weka may also have been reduced by poisoning, but they had already suffered a population crash (for unknown reasons) before the operation. Weka have become much more abundant and much tamer in the 6 years since the poisoning. While no data were collected before the poisoning, anecdotal observations suggest that other native birds (e.g., tui, fantails, warblers) and invertebrates (e.g., tree weta) have become more conspicuous since rats were removed. The understorey began growing rapidly after the eradication, and is now extremely thick. The larger gullies now have fairly mature forest with an open understorey, but the rest of the island is virtually impenetrable unless tracks are cut.

A helicopter drop of brodifacoum (Talon 7-20) cereal pellets was conducted on 18 September 1996 in an attempt to eradicate mice. This was unsuccessful, although mouse levels were reduced to extremely low levels after the drop.

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Translocations and Research

Three bird species have been translocated to Mokoia since the original rat eradication: New Zealand robins (toutouwai), saddlebacks (tieke), and stitchbirds (hihi). The populations of tieke and hihi on Mokoia are the only mainland populations of these species since last century. Research on Mokoia began when tieke were transferred from Tiri in 1992, and this population was studied for the next 6 years (Armstrong & Craig 1995; Davidson 1999). Hihi were released in 1994, and were subject to intensive research for 5 years (Armstrong et al., 1999; Armstrong & Perrot, in press). In 1999, seeds of two species of mistletoe (Ileostylus micranthus and Tupeia antarctica) were translocated to Mokoia. See the rundown of reintroduction projects for further information.

Research has also addressed the impact of the 1996 poison drop on tieke, hihi, and ruru (morepork owl, Ninox novaeseelandiae). Mark-recapture analysis was used to estimate the effect of survival in tieke and hihi. About 27% of tieke are estimated to have been killed by the poison drop (Davidson 1999), whereas there was no significant increase in mortality in hihi. Simulation modelling estimated that it only took the saddleback population 1-2 years to recover, and that the drop did not reduce population viability (Davidson 1999). An ad hoc analysis of ruru with radio transmitters suggested that about 21% of died as a result of the poison (Stephenson et al., in press). A comparison of breeding success in the seasons before and after the drop suggests that ruru had reduced reproduction following the drop, possibly due to sub-lethal poisoning. This was not observed in tieke.

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Visitors, Education and Public Involvement

Mokoia is a 15 minute boat trip from Rotorua, and is in an excellent position to allow public access to wildlife and increase public awareness. There were formerly daily trips to the island, but there is currently no boat operator visiting the island.

Since 1980, there has been an annual camp where boys and men learn taiaha, wero, hangi preparation, and use of a waka toa. Since 1987, there has also been a women's camp focusing on flax weaving, karanga, and other skills. There are also now campouts by kohanga reo and other schools.

Schools are also involved in restoration and research. Local high schools have been involved in all the bird transfers, and built wooden nest and roost boxes for tieke and hihi. Many volunteers have been involved in research since 1992. Most volunteers come from organisations such as the Ornithological Society, Forest and Bird, come from Massey University, or are travellers looking for volunteer work from DoC.

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The Future

A draft ecological management strategy for Mokoia was produced in 1998 (Dumbell 1998).

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Andrews, P. 1992. Mokoia. Bibliophil, Rotorua.

Armstrong, D. P., & Craig, J. L. (1995). Effects of familiarity on the outcome of translocations. I. A test using saddlebacks. Biological Conservation, 71, 133-141.

Armstrong D.P., Castro I., Alley J., Feenstra B. and Perrott J.K. (1999). Mortality and behaviour of hihi, an endangered New Zealand honeyeater, in the establishment phase following translocation. Biological Conservation 89: 329-339.

Armstrong, D.P. and Perrott, J.K. (in press). An experiment testing whether condition and survival are limited by food supply in a translocated hihi population. Conservation Biology.

Davidson, R.S. 1999. Population dynamics of saddlebacks on Mokoia Island, and implications for reintroduction to the mainland. MSc thesis, Massey University.

Stephenson, B.M., Minot, E.O., Armstrong, D.P. 1999. Fate of moreporks (Ninox novaeseelandiae) during a pest control operation on Mokoia Island, Lake Rotorua, North Island, New Zealand. New Zealand Journal of Ecology, in press.

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Reintroduction in New Zealand

Reintroduction Specialist Group, Australasian Section

This page was prepared by Doug Armstrong (click HERE to email), and was last updated on 13 August 1999.