Rats have taken a hit, with a drop of 80% in rat monitoring indices, and there has been a drop of 90% in indices of possum populations over four years.
The Council has targeted rats and possums in the forest as part of its work to extend the network of mountain bike and walking trails in the Kahuterawa Outdoor Recreation Area, about 17 kilometres east of the city.
"Rats are as destructive as possums," says forester, Mark Johnston. "They eat birds, their eggs and chicks, lizards, invertebrates and a wide range of native fruits and other plant material. Ship rats are good climbers, so can get access to bird nests high in trees."
The pest control programme is also giving extra protection to the native giant carnivorus snail Powelliphanta, which lives in the area, and there is a slow but steady increase in the amount of bird song heard in the area, he says.
"The area is proving to be a safe haven for native birds," says Peter Handford, manager of the monitoring organisation GroundTruth Ltd. "There are signs of an increase in numbers of Korimako, the Bellbird, and a pair of one of our most spectacular birds, Karearea, the New Zealand Falcon, are using the area."
The poisoning programme began in 2010 around the Back Track and Sledge Track areas, on both public and private land, which covers around the 250 hectares of the Arapuke Forest Park area. The cost of the programme is $15,000 which at 250ha equates to $60/ha.
Daniel Ritchie Contracting carries out the programme and GroundTruth Ltd provides independent monitoring. The controls used are feratox and brodifacoum bait, and flavoured paraffin wax blocks are used for monitoring purposes. The blocks are impregnated with pink dye and aniseed that possums and rats chew, leaving bite marks. Monitoring records the number and type of bite marks, then compares them over time.