New design of pest proof fence proving a saviour for New Zealand's wildlife.

28/04/2007 00:00:00 The future looks brighter for some of New Zealand’s most threatened wildlife following the development of a pest-proof fence which prevents access to fifteen of New Zealand’s most damaging pest animal species.

Already, endangered wildlife such as kiwi, takahe, saddleback and Mahoenui giant weta have been translocated to sites surrounded by the Xcluder pest proof fence, while habitat for white flippered penguin, grey faced petrel and grand and Otago skink has been protected. More species translocations are planned to many of these ‘safe’ sites. As each area is surrounded by the pest proof fence, a pest eradication operation is conducted to eliminate all the pests from within the enclosed area. There is then no need to constantly trap and poison pests. A post eradication monitoring regime evaluates the success of the operation and provides essential data on any remaining pest numbers.

Despair at finding that the Australian possum (an introduced animal) had caused considerable damage to 50,000 newly planted native plants prompted the owner of a 16 hectare native forest to seek a permanent pest solution. He enlisted the help of an ecologist, a fencer and an animal behaviourist, and collectively they decided the most suitable solution was a pest exclusion fence. Various fence designs were trialled and the developers spent hours watching footage, frame by frame, of the pest animal’s reaction to each design. Of the fifteen pests targeted by pest proof fences (Norway rats, ship rats, mice, stoats, cats, weasels, ferrets, red deer, fallow deer, pigs, goats, possums, hedgehogs, rabbits and hares), the mice presented the greatest challenge because of their ability to move through very small holes.

Research showed, in fact, that a 7.1mm aperture was the smallest an independent mobile juvenile mouse could squeeze through and even then it was its hips that stopped it.

The successful design is made from 316 marine grade welded stainless steel 6 mm mesh. The choice of materials ensures that the 6mm gap, with 1.1mm safety margin, remains constant regardless of weather conditions, aging or joins, and so that the fence is suitable for many habitats including coast lines. Standing at 1.95 metres high with a smooth curved hood along the top, the fence prevents pests such as cats, stoats and possums from jumping or climbing over it. The maximum 6mm gap not only stops entry by mice but also infant rats and weasels, and the mesh skirt along the ground prevents digging animals from tunnelling underneath.

As at the end of 2006 more than 80km of Xcluder pest proof fence had been erected in New Zealand on a range of habitats. A 40km pest proof perimeter fence around 3,400 hectares of native forest on Maungatautari mountain will protect a range of New Zealand’s most endangered species. The vision for the Maungatautari Trust is to reintroduce a complete suite of species to form an ecosystem as close as possible to that which would have existed before the arrival of man. The introduction of kiwi and takahe into separately fenced enclosures on the mountain has already started that process.

At the other end of the scale is a much smaller 10m by 10m fully enclosed area protecting the Mahoenui giant weta from pests.