Predator fencing is currently used in New Zealand to protect at-risk flora and fauna in small, predator-free environments, and to prevent contamination of industrial food processing plants.
Unfortunately, current predator fencing systems have limited application, due to their high construction and maintenance costs, obtrusive 1800 mm stature, and lack of mobility.
ZIP is exploring predator fencing solutions for a wider New Zealand context, particularly for use around rural and semi-urban areas.
In 2017, we began conducting trials at our predator research facility in Lincoln, Canterbury, to determine the minimum fence height required to contain possums, rats and stoats.
Custom-built 4 x 4 metre testing pen inside ZIP’s larger (2 ha) predator-fenced enclosure
Trials were run in a custom-built pen inside ZIP’s 2-hectare predator fenced enclosure. The 4 x 4 metre pen has a standard predator mesh and capping system which was able to be adjusted to be trialled at three heights: 800 mm, 900 mm and 1100 mm. 1100 mm was the highest fence tested, because this is the same height as standard sheep and cattle fencing.
Wild caught animals were given a two-week period to acclimatise to captivity at the predator research facility, before they were re-caught and transferred to the 4 x 4 metre pen. Each animal was given three nights to attempt to escape from the pen. Sustenance, water and shelter were provided throughout. More attractive food was stowed outside the pen, to encourage escape attempts. A series of trail cameras recorded animal behaviour and interactions with the fence.
At the conclusion of the three-night trial, each animal was recaptured and returned to its individual housing. Animals that escaped at 800 mm or 900 mm were re-tested when the fence height was raised; animals that were initially unsuccessful were not re-trialled.
Stoat contained by 1100 mm predator fence
Possum attempting to jump over 1100 mm predator fence
At a height of 1100 mm or lower, the fence contained 19 out of 20 stoats tested, 20 out of 21 possums, and 20 out of 20 rats.
Overall, we are encouraged by the number of individuals from each species that were contained by the lower fence height (100% of rats, and 95% of possums and 95% of stoats at a height of 1100 mm or lower).
The benefits of a reduced predator fence height could significantly alter how fences are deployed for conservation. These benefits include:
Lower deployment and maintenance costs
Lower fences use less mesh and staples than standard predator fences. They also require less intensively spaced support posts, as the reduction in height reduces both weight and wind resistance. These alterations also mean that fences are more readily able to be moved around and deployed in other regions.
Increased social acceptability
Lowering the height of fences improves their appearance, and makes them less obtrusive in the landscape. As a result, the 1100 mm fence is likely to be more suitable for use around areas where people live.
Potential ability to retrofit predator fencing into existing landscapes
Conveniently, 1100 mm is the same height as a standard stock fence. With some modification, large portions of rural and semi-urban New Zealand could be protected against invasion by fitting a predator cap and mesh onto existing fence systems.
Ability to productionise the cap components for cheaper construction
Traditional predator fencing is usually purpose built. Overall costs could be significantly reduced by productionising materials and construction techniques, to enable landscape-scale deployment.
Next steps
ZIP is trialling a range of deterrents to defend permanent openings in predator fences, to enable these to remain open for ease of human access. Detection systems and response techniques are also being investigated to remove invaders that successfully breach the fence or deterrents.
Plans are in progress to build and test a prototype low height (1100 mm high) predator fence in the Aoraki region in 2018/19. We are also investigating options for more efficiently manufacturing and constructing predator fences.
Want to learn more?
Check out the technical report.
But what about feral cats?
We are sometimes asked why ZIP doesn’t also develop tools and techniques to manage feral cats, particularly in the context of predator fences. After all, feral cats are a major concern in some ecosystems (for example in braided river systems, where they are one of the main predators of critically endangered tarapirohe/black-fronted terns and kakī/black stilts).
ZIP has retained a tight focus on possums, rats and stoats, because these three species are generally acknowledged to have the most destructive impact on biodiversity across the majority of New Zealand’s landscapes (and they are a significant challenge in themselves). Consequently, significant ecological gains are anticipated as a result of their removal.
Retaining a relatively narrow scope also enables the small ZIP team to more quickly advance toward our research and development goals. In addition, the challenges associated with managing feral cats and their impact on native biodiversity are not simply technical. Because many New Zealanders own and value cats as companion animals, the issue of cat management – particularly around areas where people live – is socially complex.