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A programme of work is underway in a 12,000 hectare block within the Perth Valley (South Westland) to test and refine an approach to completely remove possums from large areas, and prevent them from re-establishing. The work will also seek to develop this predator management approach for ship rats and stoats. If successful, the approach will have significant beneficial outcomes for native plants and animals.

It could also reduce the need for the repeated use of landscape-scale aerial 1080 to control these predators here and elsewhere in New Zealand, and help pave the way for a predator-free New Zealand.

This work is a collaboration between Zero Invasive Predators Ltd (ZIP), the Department of Conservation (DOC), and Predator Free 2050 Ltd.

The indicative boundaries of the research area are shown on the map below.

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The approach being developed has three main parts:

  1. Reinforcing natural barriers to the movement of predators into the block (e.g. rivers, alpine tops) with a network of traps.

  2. Completely removing predators within the block. This approach uses a more rigorous method of applying aerial 1080 than standard operations. The operation was originally scheduled to be carried out during winter 2018, but was delayed as a result of unfavourable weather conditions. We now propose to begin the operation in March 2019 (subject to receiving approval from DOC and the Medical Officer of Health).

  3. Detecting predators that either survive the 1080 treatment or reinvade the block from beyond its boundaries, and removing them before they can establish a population.

The work programme is evident through the presence of:

  1. ZIP field staff. Staff are regularly flown by helicopter to and around the site.

  2. traps, as well as detection devices such as chew cards and motion-sensor cameras.

  3. satellite communication facilities at Scone Hut, some temporary access routes, and three temporary bivvies (for ZIP and DOC staff).

  4. a predator gate on the swing-bridge across the Perth River near Scone Hut.

Please do not interfere with the equipment or any trapped animals because doing so will compromise the results of the research.

Kea in research area  (Chad Cottle)

Kea in research area (Chad Cottle)

Rata in flower at research area  (Devon McLean)

Rata in flower at research area (Devon McLean)

Possum eating bird egg  (Nga Manu Images)

Possum eating bird egg
(Nga Manu Images)

ZIP and DOC staff are continuing to meet with Te Rūnanga o Makaawhio, Te Rūnanga o Ngāi Tahu, local people and recreational users of the valley (particularly climbers, trampers and hunters) to identify any impacts of the research programme, and options to reduce the impacts.

An estimated 75-100 kea are present in the research area. Although 1080 has been shown at other sites to benefit kea populations, individual birds have been known to die as a result of 1080 poisoning. Consequently, the work programme includes a range of measures to minimise potential impacts of the removal operation on kea, including:

  • applying non-toxic cereal baits containing a repellent prior to the operation to ‘train’ kea to avoid baits; and

  • distributing a small number of tahr carcasses above the operational area, as a more attractive, preferred, food source.

We have also fitted bands and radio-transmitters to kea, to monitor the impact of applying aerial 1080 on their mortality and breeding success. We are also monitoring the impacts, if any, of the operation on whio, rock wren, and tahr (the latter in collaboration with the Game Animal Council and New Zealand Deerstalkers Association).

Possums are the initial focus of this work because:

  • they are known to prey on native bird species such as kereru and kea and their eggs, as well as invertebrates such as wētā;

  • they are the major cause of the decline of trees such as kāmahi and rātā; and

  • the results of similar research at smaller sites suggest it is likely that the approach described will be successful.

The Perth Valley was selected for this research because:

  • ZIP already had existing working relationships with local DOC staff;

  • the rivers and streams and alpine tops are expected to be strong natural barriers;

  • the area contains valued biodiversity; and

  • the control area is relatively accessible (by helicopter) from a road end.

To learn more about this project, please email us at info@zip.org.nz, or call ZIP’s Operations Director, Duncan Kay, on 021 069 0167.