Taranga Island and the Hen and Chicken Islands as seen from Leigh Marine Reserve

Image: Les Molloy | DOC

Introduction

DOC, in partnership with the Ngatiwai Trust Board, has completed an operation to eradicate kiore (Pacific rats) off Taranga (Hen) Island.

Taranga Island is part of the Hen and Chicken Island group on the Whangarei coastline, Northland.

Why kiore were eradicated

Kiore, the only animal pest that existed on the island, were having significant adverse effects on the ecosystem. If nothing was done, the continued existence of the many threatened species there were at risk.

Pest free islands play a vital role in providing safe-havens for many of our threatened native species. Kiore eat a wide range of food including seeds, fruits, insects, lizards, eggs and chicks.

Between 1994 and 1997 similar operations successfully eradicated rodents from the adjacent Marotere (Chicken) Islands; Coppermine, Whatupuke and Lady Alice. Today a huge difference in the abundance of native bird and lizard fauna has been observed between these islands and Taranga Island. DOC expects this will also happen on Taranga Island following the eradication.

How kiore were eradicated

Taranga Island was too rugged to be baited from the ground so cereal bait was applied from the air using helicopters with under-sung buckets. Global positioning navigation was used.

Helicopter with bucket.
Helicopters were used to bait the rugged land

Helicopters flew back and forth over the island to ensure that there was bait available where any rats may be present. This is the only practical and safe way of achieving eradication.

The bait used was Pest-off 20R™ containing 0.02gm/kg Brodifacoum (a common rat poison). This is widely used and proven to be the most effective bait for rodents. The bait is presented as cylinder shaped pellets about 2cm long and dyed green.

When the operation took place

The operation took place in May 2011. The timing took advantage of the fact that rodents were under maximum stress through lack of food and cold weather. Winter is also the wettest time of the year, so bait breakdown is more rapid and non-target species such as reptiles are at their most inactive.

Monitoring results

Monitoring was carried out in June 2012 and then again in May 2013 using rodent detection methods that consisted of tracking tunnels (an ink surface in the tunnel records the prints of any animal passing through it), rat traps, observations from people working on the island and rodent detecting dogs scouting the island.

With two years passing since the aerial application of bait and no rat sign recorded this confirms they have been eradicated.

Back to top