June 2019

FENCED SANcTUaRIES - a thought provoking review from Peter Hale

The best way to conserve endemic bird species is to place them in a predator-free ecosystem, either on an island or behind a fence. Fencing native forest remnants from stock was commonplace and in the 1980’s and 1990’s fences started to be considered in situations where species could not be transferred to predator-free sites. Around the same time many off-shore islands were successfully cleared of pest mammals. By 2008, 71 islands were clear of pest mammals and a further 65 had been cleared of at least rats.

This island experience lead DOC to create a series of "Mainland Islands" based on trying to control pests to very low levels and to limit re-invasion. Six were initiated in 1995–1996 ranging in size from 117–6,000 ha. I understand they have had mixed success. Predator control failed in some years, mice and hedgehogs were not targeted, rabbits increased after stoat and cat control, mice increased after ship rat removal and ship rats increased after possum removal Stoats preyed on more birds when rats were absent and rats preyed on more birds when stoats were absent. The predation impact on some bird species was greater after stoat control than when there was no control at all. There was also concern with toxin residues in non-target wildlife and the environment when brodifacoum (the most effective rodenticide at that time) was used.

An extensive review of all 6 “Islands “was done in 2000 and a report on 6 years of control at Trounson Kauri Park was published in 2010 but I have been unable to locate any other documentation on the history and current status of the “Islands”. A number do produce annual reports but not all are easily accessible. The major goal of the projects was to research pest control methods and apply the knowledge and experience gained to other habitat and species restoration projects. There appears to have been little information communicated in a manner that might increase the effectiveness of conservation in the wider context, especially community conservation.

The use of fences to exclude a range of predators was an alluring prospect. This started with simple fences protecting takahe and black stilt rearing areas and this led to more sophisticated designs. The upsurge in community-led conservation projects in New Zealand coincided with the development of 2 pest-proof fence designs by Xcluder Pest Proof Fencing Ltd and Central Fencing Ltd, the former in 2000 and the latter in competition in 2005.

Currently there are about 28 sites with another 10 in the planning stages. It is difficult to source an up-to-date list however this list covers the main sites and others are listed in Table 5.1 of this publication. They range in size from the Maungatautari Ecological Reserve now known as Sanctuary Mountain with 47 km of fence enclosing 3363 ha, to Rapanui Point protecting 5 ha with 0.7 km of fence.

The location of pest-proof fences was not part of a coordinated conservation strategy but has occurred independently through community groups and private individuals. The areas chosen have not generally been areas of high biodiversity, but areas of lesser biodiversity and often close to population areas which is not surprising. We all have the common aspiration of wishing to “bring the birds back to our backyards”.

While fences are predator-resistant they are not necessarily predator-proof. Fenced sanctuaries are always prone to invasion, some more so than others depending on the site. Water courses plus the surrounding landscape are problematic and peninsulas have exposed ends at the coastal interface. In 2015 a single female stoat got into the Orokonui Sanctuary after a heavy snowfall and evaded capture for several months. In that time it decimated the entire saddleback population of approximately 40 birds. A list of recorded sanctuary invasions was published in 2014.

The cost-effectiveness of fenced sanctuaries has been vigorously discussed in the media and the scientific literature but this has not halted new projects. Further reading can be found in the references listed at the end of this article.

The BIG question is do they work? This would appear to be a no-brainer to most however until recently this had not been scientifically demonstrated. This is essential for those providing the funds as with any other business venture.

Not all species benefit equally from the lack of predators as described here in Zealandia. Some species that were present but previously unknown have been able to increase to detectable levels such as Duvaucel’s gecko and Hochstetter’s frog in Sanctuary Mountain and giant weta in the Brook Sanctuary. Fenced sanctuaries have also been used as crèche’s for species such as North Island brown kiwi. They have also provided opportunities for natural dispersal and population founding events. Bellbirds self-reintroduced to the Tawharanui Open Sanctuary from Little Barrier Island after being locally extinct for more than 100 years.

As well as protecting existing populations pest-proof fences have also provided secure sites for the translocation of other species. This translocation process must follow strict DOC protocol. Communities would love to introduce some of our most iconic species, saddleback and robin being the most popular, however the site needs careful evaluation as homing instinct and dispersal to areas outside of the fence are major factors to consider. Saddlebacks have bred outside of Zealandia in the Polhill Reserve however long-term survival is unlikely. A male tomtit that was part of a translocation to Tiritiri Matangi Island flew back to his mate in the Hunua ranges, some 63 km.

Fenced sanctuaries are not popular with all members of the community as outlined here kaka , kaka and tui . The mind boggles!

Fences alone cannot save our biodiversity but they do provide mainland islands that conserve species and encourage more people to appreciate and value conservation efforts. They still require on-going management but that is the same for off-shore island sanctuaries. With all such exercises it is the challenge of trying to be more cost-effective to maximise gains from the available resources.

Further reading:

The Use and Potential of Pest-Proof Fencing for Ecosystem Restoration and Fauna Conservation in New Zealand

Fenced sanctuaries deliver conservation benefits for most common and threatened native island birds in New Zealand

Pest fencing or pest trapping: A bio-economic analysis of cost-effectiveness.

Are predator-proof fences the answer to New Zealand's terrestrial faunal biodiversity crisis?

Role of predator-proof fences in restoring New Zealand's biodiversity: A response to Schofield et al. (2011)

Fenced sanctuaries need critical evaluation: A reply to Innes et al. (2012)

Monthly Trapping Totals - Peter Hale

Below are the catch statistics for June, note the 70 DOC 200's have been removed from the ski field road so the Rainbow Valley trap number drops to 8. I have not included 5 mice that were caught in DOC 200's on the stoat lines.

Finally a company has come up with a decent roto-molded plastic tunnel for DOC 150 or 200 traps. Trapinator is a division of CMI Springs who manufacture and distribute the DOC series traps. Check out the details here: https://trapinator.com/ . For those who do not have facilities to manufacture their own trap boxes these may be an option, $80 including a stainless DOC 200 or $63.50 with a combo DOC 200. Note they utilize the "Will Rickerby" hinged- top design which we have been using for more than 10 years and they have also incorporated a bait protector which can enclose an egg or block of Erayz. I have been in contact with company regarding the problem of weka and they are currently working on a "weka length" version with a longer distance from entrance mesh to center baffle (needs to be at least 255 mm but better at 300 mm) which will be available shortly.

There will be a tunnel for display at the FOR meeting in July.


Mt Stokes Mohua- Peter Hale

Some of you may be aware of this historic story on the demise of the Mt Stokes mohua population, it is a good example of the threat currently faced by some of our most vulnerable species following the current megamast. It is important to note that mohua used to be one of the most prolific forest bird species.

Julie Robilliard