Project implementation

DOC staff member next to mature rimu
tree

Doing the work

Currently, we have five Core Areas in the project. These were set up initially to increase kokako numbers as well as help other native species. Core Areas are the main focus of our work: we control rats, stoats and possums in all five Core Areas. Feral dogs and cats are targeted in two Areas, and deer are hunted by professional hunters at Otamatuna.

Different pest species require different levels of effort to reduce their populations to low numbers. For example, rats require dense settings of traps (e.g. every 25m along trap lines) to reduce their numbers to low levels.

Rat territories are small and they breed often, and so they can repopulate areas very quickly. Stoats on the other hand roam very widely and so traps can be spaced further apart. How many traps to put out, how often to check them, and what kind of baits to use are examples of information that we are trying to learn within the Mainland Island.

The on-the-ground restoration work generally falls into two categories: pest control and monitoring. Most of the pest control work is done by contractors managed by DOC staff. DOC staff undertake most of the monitoring work themselves.

We monitor several indicator species as a gauge to determine how well our pest control work is proceeding. Included are:

• Kokako - a threatened forest bird whose eggs and chicks are often killed by rats and possums
• Young kiwi and whio (blue duck) which are vulnerable to predation by stoats
• Native mistletoes (Peraxilla tetrapetala and Alepis flavida) which are favourite foods of possums

If we find that these species are doing well then we assume that other plants and animals that are also preyed on should be doing well.

Pest overview map
(view larger, JPG, 260K)

We also monitor other aspects of the forest ecosystem such as:

• The number and diversity of forest birds,
• The condition of tawhero (kamahi) (Weinmannia racemosa) a common forest canopy tree,
• The abundance of rats, possums and deer,
• The number of seedlings preferred by deer

Currently, we do:

• Annual possum control over 9900 ha,
• Year-round rat control over 580 ha and seasonal rat control over a further 920 ha,
• Stoat trapping over approximately 7800 ha where traps are spaced every 100 to 200 m,
• Cat control using a network of traps spaced at 500 m within the adjacent Otamatuna and Mangaone Core Areas (4000 ha),
• Control for feral dogs using traps located at key sites within Otamatuna and Mangaone Core Areas,
• Deer control in the Otamatuna Core Area (2500 ha)

When you look at the map showing where we do our pest control it shows that we target several pest species at each Core Area. For example, in the Otamatuna Core Area (2500 ha), possum, deer, stoat, cat and dog control is done over the whole area, and year-round rat control is undertaken over 580 hectares in the centre of the block.

Because of the way we control animal pests (i.e. using traps and hunting), access tracks are very important. About 450 km of cut and marked tracks (including some public tracks) are maintained to allow access for pest control and monitoring. Because access is limited, seven DOC management huts and numerous public huts are used by staff and contractors for overnight stays.

Progress to date

This project has already made strong gains in ecosystem recovery and learning. Populations of several threatened species have recovered or have been maintained. Ongoing pest control has provided benefits for many other species.

Probably the most significant indication of the success of the project so far is the increase in the number of kokako pairs in the Otamatuna Core Area. Kokako protection at Otamatuna was one the key reasons the project was established. Here, numbers had fallen to as low as eight pairs by 1993. With the increased protection afforded by the establishment of the Mainland Island in 1996, kokako numbers increased steadily to the point where in 2006 there were an estimated 112 pairs. Kokako recovery at other Core Areas has not been as spectacular, however, we now have an estimated 170 pairs in areas where there is rat (in part), stoat and possum control, up from 50 pairs in 1996.

Rat trap

Other successes in the project include:

• A significant increase in the number of whio/blue duck in Te Waiiti Stream (6 to 28 pairs)
• An increase in the abundance of kereru/New Zealand pigeon (2.6-fold increase from 1997 -2001)
• An increase in the number of mistletoe (Peraxilla tetrapetala) plants in Otamatuna, from 10 in 1996 to 81 in 2001
• A significant population of kiwi (c.100 pairs) being protected
• Improved canopy condition of kamahi has indicated that possum impacts have been reduced

In parallel to the gains in ecosystem quality, there has been a large amount of knowledge gained about ecosystem restoration methods in a large forested area. Perhaps the most notable achievement has been developing the use of traps as a principal control method for animal pests. In many mainland ecosystem restoration projects in New Zealand there is a significant reliance on the use of various toxins, and in large, back country areas the aerial distribution of toxins (e.g. 1080) is a commonly-used method.

Within Te Urewera Mainland Island a strong emphasis has been placed on the use of traps for the control of possums, stoats and rats. This emphasis has provided an invaluable learning opportunity as to the effectiveness of various traps and trapping regimes for controlling pest animals to acceptable levels. Many lessons, especially those associated with using trapping as a principal control method, have been passed on to other conservation managers, and many of the findings have been absorbed into DOC best practice methods, especially for rat trapping.

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