Giant Gecko Rediscovered - One of New Zealand’s heavyweight lizards hangs on by Trent Bell
Environmental News Issue 24 Summer 2011

Who’d have thought? New Zealand’s largest living gecko species, and one of the world’s largest geckos, has just been rediscovered at Windy Hill Rosalie Bay Catchment Sanctuary in January this year - albeit unfortunately dead in a rat trap. Field worker Rachel Wakefield discovered the decomposing lizard during a routine check of trap and bait stations. With the aid of a lizard field guide, she was able to identify it as a Duvaucel’s gecko and this was verified when the preserved remains were sent to Halema Jamieson.

Duvaucel’s gecko (Hoplodactylus duvaucelii) are very large and heavy-bodied geckos, with the largest recorded specimens reaching to 32cm long, and up to 118g. Although chevron skinks are known as one of New Zealand’s longest lizards, they are not as fat or heavy (40g). This discovery comes on the heels of the rediscovery of the rare striped skink (Oligosoma striatum) near Windy Hill in 2009.

What is the significance of this rediscovery? The last – and only – recorded and verified sighting of Duvaucel’s gecko on the Barrier was exactly 40 years ago in 1971, by Brian Gill of the Auckland Museum, at Okupu. The closest existing pop-ulations are those of the Mokohinau Islands in the north, Little Barrier Island and also the Mercury islands to the south. Anecdotal rumours do persist of ‘large lizards’ being seen on Great Barrier Island on the odd occasion but these are usually attributed to chevron skinks.

However, sightings last year of ‘very large gecko’ in Okupu may have been a Duvaucel’s. Have Duvaucel’s geckos on Great Barrier Island survived the onslaught by the pirates that ship rats are? That was considered highly unlikely, but in light of the rediscovery, is now clear that at least a few have.

Duvaucel’s gecko were once widespread on the New Zealand mainland, with subfossil or museum records indicating presence in Northland, Waikato, Hawke’s Bay, Wellington, Canterbury and even Otago. Distressingly, the species’ current range is now disjunct, with a 400 km straight line gap between the closest north-eastern island populations and the southern island populations on the opposite ends of the North Island. (NB, the Maungatautari gecko found in a rat trap has been determined by genetic analyses as most likely have been a released captive-bred animal). The extinction of Duvaucel’s gecko on both the main islands, and some offshore islands is attributed to predation by rats, cats and mustelids.

So what puts such large geckos at risk of rats and other predatory mammals? It is thought that Duvaucel’s gecko faces enhanced risks from predation by rats due to a combination of factors. As the geckos are strongly nocturnal (active at night), their activity period coincides with rats, a time where the geckos are most vulnerable while they are foraging for food or mates without protective and secure refugia nearby. In order to ‘escape’ predators, Duvaucel’s gecko run and ‘freeze’, a strategy probably effective for birds, but clearly not very smart when encountering rodents and cats.

Another vulnerability that Duvaucel’s gecko have are their own large sizes. Being too fat to squeeze into many of the narrow protective refugia often available to the many other smaller gecko and skinks leads to limited avenues for escape and protection from predation. This is especially problematic for heavily gravid female geckos that often look rather obese, and waddle rather than scurry when attempting to escape!

Duvaucel’s geckos are also extremely long lived, probably the longest living gecko species in the world. Most geckos in the world live about several years, but an individual Duvaucel’s gecko was recently recaptured 50 years after being first marked as an adult in 1958 on the North Brother Island, and is possibly still alive even today. Other individuals have also been recaptured after 36 and 43 years since their first capture.

Long-lived species must therefore reach maturity later in life? Yes, that would be correct for this species. In order to breed for the first time, a female Duvaucel’s must wait six years before she is sexually mature, and a male also matures at around seven years. Duvaucel’s gecko also have a ‘low reproductive output’ – in other words it has been estimated that females have 1.12 young per year on average, and that every female only breeds every other year.

A study on Ohinau Island prior to and six months after the removal of kiore from that island found that only 4% of their population was under 100mm SVL (an adult Duvaucel’s range in size from 100mm to 161mm snout to vent length, SVL). This contrasts with kiore-free Korapuki and Green Island populations comprising of 20% and 14% newbies under 100mm SVL. Were the kiore taking the mokopuna of these geckos? As there are no other invasive mammal species on Ohinau, it is apparent that Duvaucel’s gecko populations cannot sustain themselves even from the seemingly innocuous kiore. It is also likely that in the face of the presence of the more voracious ship rats elsewhere, no Duvaucel’s gecko are able to survive long enough to even get their leg over to carry on the family line and inheritance.

Research has indicated that on kiore-inhabited islands, Duvaucel’s gecko populations were restricted to shore and cliff habitats, and nearly absent in forest. Interestingly, upon eradication of kiore on Ohinau, nearly 70% of Duvaucel’s gecko suddenly switched their habitat within six months, by leaving their cliff-bound coastal refuges to explore the forests that once comprised part of their kingdom. The geckos also spent less time in their predator-secure refugia and also came down to the ground more often. Did a similar phenomenon occur with the Duvaucel’s gecko caught in a rat trap in forest at Windy Hill, about 3 kilometres away from the Rosalie Bay’s rugged coastal bluffs, where a remnant population may potentially still exist? This may indeed be the case.

So what do Duvaucel’s gecko do in their spare time? The species is a habitat generalist occupying coastal boulders, bluffs, scrub and also forest, and is both arboreal and terrestrial. These geckos like to take up refugia in hollows, crevices and even the odd empty petrel burrow. Dietary analysis indicate that these geckos feed on a variety of invertebrates, including moths, weta, crickets, cockroaches, beetles and earwigs. However, this is when things start to get really interesting. Duvaucel’s gecko have been observed congregating on pohutukawa, ngaio and flax in bloom, engorging themselves on nectar, and thus spreading pollen to other trees, considering the pollen’s tendency to attach to the gecko’s chins, undersurfaces and limbs for at least 12 hours, and the geckos ability to disperse to distances greater than 50 m in short time frames. The ecological services of this gecko do not end there. They also feed on fruits of several tree and shrub species, and excrete viable seeds in what is often a suitable location for germination. The sweet tooth of Duvaucel’s gecko seem to know no limits, with geckos also recorded feeding on honeydew on ngaio and kanuka. As such is their appetites, Duvaucel’s have also been recording eating other geckos and even shearwater eggs. Since Duvaucel’s gecko have been recorded in densities up to 750 geckos per hectare on some predatory mammal-free islands, they must have played a very important role in many ecosystems in which they formerly occupied.

Duvaucel’s gecko are thought to have large home ranges, although as no precise estimates are available yet, this is probably around 200-500m2. These geckos can cover great distances, with one animal on the Poor Knights islands recaptured 77m away from the original capture location three days earlier. In another account, a gecko released on Mana Island was found 1 kilometre away from the release location! Yet, despite the gecko’s apparent ability to range far and wide, they also show tenacious site fidelity, with a single animal relocated in the exact same refugia on the North Brother Island after 36 years! Not only do they like their homes, they also like to share.

Duvaucel’s gecko like to aggregate, and often appear to have a ‘family group’ of geckos sharing the same crevice, potentially suggesting paired adults along with differently-aged offspring or a tolerance for younger geckos.

The news is not all bad for Duvaucel’s gecko. The gecko is still widespread and abundant along the (mainly rat-free) north-eastern islands and on several small islands in the Cook Strait. Duvaucel’s gecko have also been reintroduced to Mana Island, Tiritiri Matangi and Motuora Islands, where they appear to have successfully established.

Unfortunately, it is highly unlikely that the Barrier’s newly rediscovered gecko species are currently able to sustain their own mokopuna - or even themselves. Although Duvaucel’s gecko populations seem to have somewhat persisted on the Barrier to date, these populations are almost certainly doomed. The rats will get to them eventually, if we don’t get to the rats first.
The rediscovery of Duvaucel’s gecko as yet another piece of the rare taonga of Aotea also brings home the realization that in order to preserve all of the faunal elements of the Barrier into perpetuity, the rats must go. The question is not if, but when?

Since we have already lost the tuatara, kokako, hihi, rifleman, and saddleback, among other species from the Barrier, we cannot afford any more of Aotea’s treasures to be further plundered. As long as the impasse over the rats remains, we run the risk of losing even more of our valuables.

For those who want to find out more about Duvaucel’s gecko, a visit to Landcare Research’s NZ Lizards Database is well worth the time (http:/nzlizards. landcareresearch. co.nz). Click on the Species Synopses tab to reach a list of NZ lizard species, and look for Hoplodactylus duvaucelii. For references to the facts within this article, contact Trent.

TRENT BELL is a consultant herpetologist with EcoGecko Consultants. He is a frequent visitor to the Barrier, with a long-term lizard monitoring programme at Windy Hill. Trent is also following up a Duvaucel’s gecko translocation to Mana Island, Wellington. Trent may be contacted at trent@ecogecko.co.nz, or visit his website at www.ecogecko.co.nz