Our predator control work
The Trust undertakes sustained and intensive predator control over a vast area of the lower Hollyford – initially 2600 ha, now 12,000 ha – creating a sanctuary where mammalian predators (stoats, rats and possums) are kept to very low levels enabling native flora and fauna to recover.
Our predator control network is serviced by over 350km of lightly cut and marked tracks, which require regular maintenance to keep them serviceable.
Stoats
Stoats are controlled through an intensive grid of more than 1500 DOC200 traps, set at 400m by 200m intervals in the core area, and every 100m along traplines in the surrounding area, to ensure continuous suppression of this mammalian predator. The traps are serviced 7-8 times per year, or sometimes more if required.
The Trust has also set up a trapping loop to protect the tawaki/Fiordland crested penguin breeding colony to the north of Whakatipu Waitai/Martins Bay. Tawaki chicks are vulnerable to predation from stoats when ashore during the breeding season, and when moulting. To protect tawaki (and other birds and animals in the area), A24 traps have been set every 100m along the coast to the north of Atua Rere/Long Reef, and every 200m over the ridge back to Martins Bay. This project has been funded by the Cliff Broad Memorial Fund. Please see the Cliff Broad Memorial Project for more information.
Trail cameras have been shown to be an effective tool for monitoring stoats. The Trust maintains a trail camera network for monitoring stoat abundance.
Possums
Until recently, possums were considered pests due to their effect on native flora, but they are also predators of native birds. Possums are known to feed on birds’ eggs and invertebrates and have been recorded destroying nests of kererū and killing both adult and young fantails. Possums also restrict the food sources of insectivores such as tomtits and robins by predating on invertebrates.
Early aerial 1080 drops in the lower Hollyford were critical in the initial ‘knock-down’ of possums. Together with ground-based control undertaken by the Hollyford Conservation Trust, possum levels have now been reduced to very low levels, and this has allowed palatable species to recover, restoring an important food source for native birds and other fauna.
When required, possums are controlled using Feratox bait which is put in the bait stations.
Possum monitoring is undertaken every few years using the Possum Trap Catch method (RTCI).
Aerial 1080 pest control
DOC’s Battle for our Birds (BfOB) Tiakina Nga Manu programme has undertaken aerial 1080 pest control in the Hollyford Valley in 2015, 2017 and 2019, targeting possums and rodents (with an anticipated secondary kill of stoats). The September 2015 operation encompassed 18,000 ha, which was expanded to 43,000 ha in September 2017, covering both the lower and upper Hollyford Valley. Both aerial operations included the HCT project area and have been shown through monitoring to have had a beneficial knock-down of possum, rodent and stoat populations within the treated area there. In 2019, the area was reduced due to budget constraints. The middle Hollyford was not treated, and the lower Hollyford was reduced to the initial project area (2600ha) plus a one-kilometre buffer – approximately 5000ha in total.
Aerial 1080 is an effective tool assisting with the predator control programme in the Hollyford.
Rodents
The Hollyford Valley has two species of rat: kiore, Rattus exulans, and the ship rat, Rattus rattus. It’s unusual to have kiore on the New Zealand mainland and their smaller home ranges require a different control approach.
In our project area we use a grid of more than 2100 bait stations to control rodents and possums. The bait stations are located every 100m throughout the central project area so that there is at least one bait station in the home range of every rat.
In the higher productivity areas, rat control is intensified with additional bait stations and an A24 network. Rats are also caught in our DOC200 traps.
Pre-season rodent monitoring is undertaken to determine rodent levels in the area. Bait is typically put out from August to October to coincide with the start of the bird breeding season and used thereafter to control rats based on subsequent monitoring results. It is imperative that we work to ensure low densities of rats during the bird breeding season.
Rodent monitoring is undertaken a minimum of four times a year in February, May, August and November, in line with DOC’s rodent monitoring at adjacent sites. We have a network of 15 monitoring lines each with 10 tracking tunnels across the project area, as seen in blue on the map below. The results inform our pest control operations.
Bait is typically put out from July to coincide with the start of the bird breeding season and used thereafter to control rats based on subsequent monitoring results. It is imperative that we work to ensure low densities of rats during the bird breeding season.
