Proof-of-concept: The small fence
With their vision of re-introducing locally extinct lizards to Central Otago, Mokomoko Dryland Sanctuary was embarking on pioneering work. Re-introducing grand and Otago skinks and establishing a self-sustaining population in a predator free area hadn’t been done before. As such, it was seen as high risk. Before embarking on the full-sized sanctuary they hoped to eventually create, the Central Otago Ecological Trust (COET) first needed to establish that such a thing was possible.
So in autumn 2009 work began on a 180 m long fence at the Mokomoko Dryland Sanctuary site. Enclosing 0.3 ha of prime lizard habitat, this pilot project would be the smallest predator proof sanctuary in the country!
By the end of winter 2009 the fence was complete. It was two metres high and designed to exclude all mammalian pest species, with mesh fine enough to exclude even juvenile mice. Over the next few months this small sanctuary was cleared of pest species through the use of both poisons and kill-traps. Approval was gained from DOC and the Ministry of Health, and methods were selected that would minimise both animal suffering and the risk of poisoning non-target species.
While the fence was being prepared for them, the captive Otago skinks were undergoing preparations of their own. For six weeks they were quarantined and screened for disease by Macraes Flat DOC under the care of Lesley Judd.
Enclosing 0.23 ha of prime lizard habitat, this pilot project would be the smallest predator proof sanctuary in the country!
Digger prepares the fence-line of the small sanctuary 2009. Credit: COET
The small sanctuary with the fence-line cleared. Credit: COET
The small fence goes up, snaking through the large schist outcrops. Credit: COET
The 180 m fence of the small pilot sanctuary is complete. Credit: COET
In November 2009 twelve captive-reared Otago skinks were released into the small fence, into a little piece of pest-free dryland Otago. The Alexandra community was thrilled to welcome these lizards back to their homeland. Release day was a celebration, with karakia (prayers), mihi whakatau (greetings) and speeches before the skink-shaped ribbon was cut and Mokomoko Dryland Sanctuary was officially opened.
The skinks settled into their new home on the generously-creviced rock outcrops, and over the summer months 11 of the 12 were re-sighted, an encouraging beginning. It looked like they were in good health, and feeding on wild insects and fruits.
Listening to the opening speeches. Credit: Donald Lamont
Jan Kelly cuts the opening 'ribbon', a cardboard Otago skink created by Alexandra Primary School pupils. Credit: Donald Lamont
Volunteers prepare trays of food to help the skinks until they can find food sources for themselves.
Credit: Donald Lamont
Be free! An Otago skink is released back into the Central Otago wild inside the small sanctuary. Credit: Donald Lamont
Although the beginning signs were promising, the real tests were still coming. Translocation is a difficult thing, as it forces animals to live in a place they haven’t themselves chosen, and can cause them a lot of stress. Many translocations around the world fail. COET knew that the real tests would be whether the skinks survived the winter in the wild, and whether they would breed.
By the end of the following summer (February 2010) they had the beginnings of an answer. Nine skinks had survived their first year, making it through the depths of winter. On top of this, three baby Otago skinks were sighted in different parts of the sanctuary, which suggested that a number of females had given birth. It looked like they were on the way to establishing a population.
The real tests would be whether the skinks survived the winter in the wild, and whether they would breed.
The problem of mice
Given this success, in December 2011 sixteen new Otago skinks were released into the small sanctuary, including some offspring of wild skinks which were hoped to improve the genetics of the population. However, ten days later mice were found inside the fence. Every predator proof fence in New Zealand struggles to exclude mice, and this one was no exception.
At first COET was not too worried. Recent research by the Department of Conservation had shown that grand and Otago skink populations recovered when the larger mammalian pests were removed but mice were still present (albeit at very low densities during most years). This research was leading COET to consider changing the design for the planned 14 ha fence to a cheaper design that ‘leaked’ mice. They began to get quotes for this new design. (To read a comparison of the cost-effectiveness of trapping, leaky fences or full exclusion fences see Norbury et al. 2014).
However all this changed when two Dutch students were monitoring the skinks at this time. They witnessed two incidents of mice attacking 25 cm long adult skinks. Both skinks escaped, but the one they re-sighted two hours later had a bloody wound on its head. When they followed the survival of this second release cohort of skinks over the next few months, the results were alarming. Whereas the first release group were showing a survival rate of about 80%, survival of this new group which had been released as the mice entered, plummeted to about a third of this.
This was an important discovery. Grant Norbury and the students Michiel van den Munckhof and Sophie Neitzel published the results of their observations in a paper in the New Zealand Journal of Ecology. While painful learning for the Trust, it would be a valuable alert to other groups. It suggested that efforts to exclude mice in lizard translocations were warranted, at least during the first phase of a translocation while the lizards were settling in. Mice are especially damaging in these modified grasslands because introduced grasses and herbs produce abundant seed every year, which maintains very high mouse numbers.
It was thought that the first release group of lizards, who had been in the small fence for over two years before the mice entered, had survived much better because they were familiar with the terrain and had established themselves in well protected retreats.
Needless to say, thoughts of building a 14 ha fence that leaked mice were immediately dropped. A fully pest-proof fence was required.
They witnessed two incidents of mice attacking 25 cm long adult skinks.
Errol Kelly releases one of the ill-fated cohort of skinks in Dec 2011. Credit: COET
Gaps discovered in the small fence 2011.
One of the Otago skinks that was attacked by mice, showing a bite mark on its head. Credit: COET
In the summer of 2013-14, the Department of Conservation decided that the small population of grand and Otago skinks that survived in the wild in western Central Otago was at too great a risk from predation to continue in the wild any longer. They completed a salvage operation, removing the majority of these into captivity. The hope is that in time they can be returned, once the technology and resources are there to carry out landscape-scale predator control in this difficult terrain.
At Mokomoko Dryland Sanctuary, the Trust got ready to receive some of these skinks. The captive-bred Otago skinks were removed from the small fence and returned to the captive breeders. The experimental purpose of their introduction had been completed. It had been proven that Otago skinks could be re-introduced into a pest-proof sanctuary and establish a self-sustaining population. They were ready to try another experimental re-introduction, this time of wild grand and Otago skinks.
In late 2014, 15 of the western Otago skinks and 30 of the western grand skinks were released into the small fence at Mokomoko Dryland Sanctuary. However this translocation of western skinks was nowhere near as successful as the first translocation. COET and DOC suspected that they had overshot the carrying capacity of the small fence. They had released 45 skinks, quite a large number in the 0.3 ha, and they had released the grand and Otago skinks together. They usually occur in separate habitats in the wild, so they would have been competing for refuges and food.
Again, this was taken on as important learning. For future translocations within the large fence, they would aim for releasing smaller numbers of skinks at a time, with grand and Otago skinks being released onto separate rock outcrops to reduce competition.
They were ready to try another experimental re-introduction, this time of wild grand and Otago skinks.
Tom Lamb releases one of the western Otago skinks in 2014, watched by Mike Chillingworth (Auckland Zoo) and John Keene (DOC Alexandra). Credit: COET
During this phase of experimental translocations within the small fence, preparations were being made for the establishment of the larger fence. The hope was that if their piloting work within the small fence proved successful, they would have the go-ahead for the next phase, the full 14 ha Mokomoko Dryland Sanctuary. To this end COET gained funding for a herbivore-proof fence that would enclose the area of the proposed larger sanctuary. This fence excluded grazing animals such as rabbits, hares and possums, and meant that COET and volunteers could prepare the land by planting good numbers of native shrubs such as Coprosma, Olearia and Melicytus, along with native dryland trees such as kowhai and totara.
The 14 ha herbivore fence excluded grazing animals and allowed for native vegetation to begin to be restored. Credit: COET
Planting, April 2010. Credit: COET
Volunteers turned out a number of times each summer to help with planting and weeding field days. Credit: COET
During this piloting phase, the Central Otago Ecological Trust were acknowledged by several awards. In 2010 they were the regional winners for Heritage and Environment at the TrustPower Community Awards. In the same year they won the Otago Conservation Award from the Department of Conservation.
In 2012 they won the supreme award for Otago at the TrustPower Community Awards, and attended the National TrustPower Community Awards in Waitangi. COET has always been hugely grateful for the volunteers and supporters who have made their work possible, and see these awards as a tribute to the hard work and generosity of all those who have been part of the project.
COET sees these awards as a tribute to the hard work and generosity of all those who have been part of the project.
COET Chair Grant Norbury, trustee Tom Lamb and Alexandra Mayor Tony Lepper at the National TrustPower Community Awards 2012.