The success of Zealandia depends on our ability to exclude mammalian pests, including domestic pets, permanently from the sanctuary valley. Zealandia’s fence is the most effective protective barrier against key mammalian predators in New Zealand, but requires modification to successfully exclude mice.

Why a fence?

Because of the urban location of Zealandia, there was concern about the future effects of ongoing poison operations and also a need to protect threatened species from domestic pets. It was decided that a fence was the only viable option to secure the site against reinvasion.

The fence is designed to exclude more than 13 species of mammalian pests that have been found in and near the sanctuary valley.

It has been built with durable, robust materials, to withstand the Wellington climate, the daily wear and tear of an urban environment and to be easy to maintain. The design does not rely on electrification.

Design trials

A group of 22 conservation managers, scientists and engineers got together in 1993 to study a variety of existing fence designs. None proved suitable for our needs so the decision was made to design a totally new predator exclusion fence.

An extensive programme of animal trialling began in 1994. The trials tested a range of animal capabilities such as jumping, climbing, digging and their ability to pass through different size gaps.

Species	Reason tested	Components trialled
Possum	Superior climbing ability	Top hat, wall (height)
Cat	Highest jumper	Wall (height)
Norway rat	Most active burrower	Skirt
Stoat	Best jumper of all the smaller animals. Behaviour generally unknown.	Wall (height and mesh), skirt (hat)
Mouse	Small size	Wall (mesh)

These trials resulted in several prototype designs that were then tested against nearly 200 animals (including rats, mice, cats, stoats, possums, weasels and ferrets).

Finally we looked at issues like materials, installation costs, wind and visual effects. The trials resulted in four distinctive designs.

The chosen design is the simplest, most robust and easiest to install. There are three parts to the design:

• curved top hat
• wire mesh wall
• underground skirt

Materials

The fence is made of a tight wire weave mesh with a minimum gap of 6x50mm which was thought to exclude mice. At the base a woven mesh skirt extends outwards below the ground for 400mm. The skirt has proved to be an effective barrier to all burrowing animals.

To stop jumping animals the fence only needs to be 1.8 metres high. However the fence has been built alongside a popular recreation track so for safety reasons the height has been raised to 2.2 metres.

All materials used in construction of the fence are extremely strong to prevent vandalism and should last 20 years before needing replacement.

Construction

Detailed design work was completed in 1998 and construction of the fence was completed in August 1999. It is formed on the inside of a 3 metre wide track and is 8.6 kilometres long, completely enclosing the Karori Reservoir Valley.

Gate entry

Public entrance to the sanctuary valley is at a single, heavily monitored entrance at Waiapu Road.

To assist with the pest free status of Zealandia, all bags carried by visitors and staff must be emptied and repacked before passing through the gate in the same way that visitors to Little Barrier or Kapiti Island sanctuaries do.

Monitoring

However, there is always the possibility of mechanical failure, breaches of the fence or subsidence allowing re-invasion, so ongoing monitoring of the fence, ground and vegetation, as well as having strategies to detect and control re-invasions, are a permanent and very important part of the management of Zealandia.

Interested in building your own pest-exclusion fence?

Predator Fence Information (PDF)