PEST CONTROL

Foreign pests introduced to New Zealand with human colonisation have seriously depleted native wildlife and caused many extinctions. Of the endemic birds and other wildlife that remain, many are endangered.

Toutouwai in Puketi

Experience in New Zealand has shown that with good control of predator and competitor pests, a substantial increase in birdlife will occur.

Due to its size and maturity, Puketi Forest provides good habitat for a variety of native wildlife species not currently in the forest, but found there historically. This means that the prospects for successful translocations to bring back the lost species to Puketi are good.

The first steps in a successful reintroduction strategy are to establish effective pest control and to demonstrate that adequately low pest numbers can be maintained.

What pests are present?

Mustelids (stoats, ferrets and weasels), rats, possums, feral cats, hedgehogs, pigs and dogs all predate birds or their eggs and other native animals in Puketi.

Rats, possums, pigs, goats and mice consume the plants of the forest and compete with birds and other native wildlife for food.

All of these animals have been brought to New Zealand by humans.

Because of its diversity and warm climate, Puketi provides introduced mammals with a relatively abundant food supply all year. The seasonal and annual fluctuations of food supply that occur in southern New Zealand forests are much less noticeable – in Puketi it is almost like a “mast” year every year, and a high level of pest control must be maintained continuously.

Introduced predators - illustration by Cecilia Russell

Illustration ‘Puketi Forest Predators’, by Cecilia Russell

Trapping

Since 2003 the Trust’s focus has been on the control of cats and mustelids within 5500 ha of Puketi Forest (the management area) and the control of rats and possums in a 650 ha core area within this. [See Map of the Management Area] Eradication of these predators from Puketi is not feasible at present, because it would not be practicable to fence the boundary of the forest and re-invasion cannot be prevented. Continuous control to levels that allow protected species to prosper must therefore be maintained.

The primary method of control adopted by the Trust is trapping. Bait stations are installed throughout the core area so that toxins can be used to supplement trapping for rat and possum control.

The ten stoat trap lines in Puketi Forest are an average length of 10 kilometres, a day’s work for a fit trapper. (S10, serviced by volunteers, is 6 kilometres long.) Trap lines within the core area are spaced 100 metres apart. Where possible, trap lines follow existing roads and tracks, but almost 160 kilometres of additional tracks have been cut.  Regular maintenance is required to clear tree falls and regrowth.

Trap types are shown in the table.  Mustelid traps are baited with salted possum meat during summer and eggs during autumn and winter. Cat traps are baited with fresh minced rabbit or possum meat. Rat and possum traps are baited with peanut butter or proprietary non-toxic lures from Connovation Ltd: Ferafeed 213 for rats and Ferafeed Smooth for possums. Stoat lines are serviced 12 times a year, every 6 weeks during winter and every 2 weeks during summer. Core area trap lines are serviced every 4 weeks (13 times a year).

Rosters of volunteers service trap lines S10, P1, P2, T7, T8 and the Puketi Scenic Reserve. The longer and more remote trap lines are beyond the capacity of regular volunteers and are serviced by contractors. Stoat line contractors are Kelly Coogan, Tristan Kogler and Max Simich.  The core area is divided into three contract areas, serviced by Tristan Kogler, Jake Sumner and Christina Holvast. Most of Puketi is now closed to the public to reduce the risk of visitors introducing kauri dieback. The Trust’s volunteers and contractors are required to follow strict hygiene protocols.

Trap catch results are summarised on the Trapping Results page.

All traps meet the National Animal Welfare Advisory Committee guidelines for humane traps.

Ship rat in Victor Professional trap

Ship rat in Victor Professional trap

Traps Installed:

Target No. of Traps Trap Type Spacing on Trap Lines
Mustelids 1046 DOC200,
DOC250
100m on stoat trap lines
Feral Cat 256 SA1 (Coney Bear),
SA2 Kat Trap,
Timms
400m on stoat trap lines
Rat 2460 Victor professional,
Snap-E
50m in core area
(25m on boundary trap lines)
Possum 2370 Trapinator 100m in core area, 50m on stoat and possum trap lines

Stoat and rat traps are contained within boxes to prevent access by birds. Cat and possum traps, and bait stations, are mounted on tree trunks above kiwi reach. To date there have only been a few non-target casualties, mainly blackbirds, mynas and harriers. This compares favourably with estimated rates of secondary poisoning in operations using poison. No domestic cats have been caught.

Trapinator possum trap

Trapinator possum trap

Stoat in DOC200 trap

Stoat in DOC200 trap

Snap-E rat trap and box with pig-proof door

Snap-E rat trap and pig-proof box

SA2 Kat Trap

SA2 Kat Trap targeting feral cats

Supplementary Toxins

Initially, trapping alone controlled rats in the core area to the target level (less than 5% tracking), but after about four years the tracking index increased to 20-30%. Since 2012, rat trapping has been supplemented with a single annual pulse of Pindone cereal pellets in the bait stations.  Only small quantities of toxin are required because rat numbers are already substantially reduced by trapping.  300 grams of bait are placed in each internal bait station and 600 grams in perimeter stations.  Baits are checked and topped up if necessary 10 days later and all remaining bait is removed after two months.  At least half the bait put into bait stations is eventually recovered and carried out of the forest for safe disposal.

Pindone is put out during August – October to coincide with the start of the bird breeding season. Monitoring has confirmed that this is effective.

Bait station for delivering toxin to rats

Bait station for delivering toxin to rats

The Department of Conservation provides the principal effort for control of goats, pigs and dogs. No wild dogs are known to be present. Most dogs that enter the forest are brought in by pig hunters. Control of dogs is therefore via education and permitting for pig hunters, and kiwi aversion training for their dogs.