Department of Conservation pest control in Pirongia Forest Park

A bellbird (korimako), one of the bird species preyed on by ship rats at Waikato's Mt Pirongia. Photo / Manaaki Whenua Landcare Research

Protecting forest canopy and native bird habitat is the focus of an upcoming Department of Conservation predator control operation at Pirongia Forest Park.

The park contains nationally significant examples of ecosystems and threatened taonga species, including grey warblers, fantails, tomtits, pipits, harriers, kingfishers, New Zealand falcons, kererū, tūī, rifleman, bellbirds and whiteheads.

North Island robin and kōkako have recently returned to the maunga and translocation programmes continue to ensure the survival of their populations, says Daniel Heinrich, DoC's regional director for Hauraki Waikato Taranaki.

"Mt Pirongia is also home to the nationally critical long-tailed bat, and Dactylanthus taylorii/pua o te reinga, a small native plant which is parasitic and grows underground. We must do everything we can to support those species by controlling predators."

The Mt Pirongia control operation involves use of cereal pellets containing 1080 – a toxin approved for the control of pest species such as possums, rats and stoats. Applied aerially, 1080 is the most effective control method over large areas, and only viable method in remote, rugged terrain, says DoC.

Ground- based trapping and bait stations are effective in smaller more accessible areas – and community groups around the maunga are supporting DoC with this work. Aerial 1080 supplements the ground-based work targeting pests.

At Pirongia, control of possums will also limit browsing damage to native flora and fauna, and loss of forest canopy.

DoC monitors possum numbers through the Residual Trap Catch Index (RTCI) method – expressed as percentage of trap-nights in which possums are captured over set trap lines in a monitored area.

Monitoring over the past 20 years shows a long-term downward trend of possum numbers on Mt Pirongia, with DoC's pre-control monitoring in January showing an RTCI of 5.4 per cent.

An RTCI above this level is damaging to the forest species – so continued pest control gives DoC an opportunity to maintain benefits of low possum numbers.

Daniel says DoC partnered with Waikato Regional Council on engagement with iwi and the local community. WRC also carries out pest control on private land adjacent to Pirongia.

"DoC is transparent about its use of this product and shares information directly with communities and neighbours, and via its website www.doc.govt.nz."