Living on the edge
New Zealand hosts the longest-lived geckos on the planet and was once home to the largest, the kawekaweau of Maori folklore. And as we learn more about our geckos with every study, the stranger and more extraordinary they appear.
New Zealand has long been known as the “land of birds”. Feathered fauna defines our natural heritage and birds such as the kiwi, kakapo, kea, fantail and ruru are scattered through our material culture, adorning everything from clothing to teaspoons. But when it comes to ecological contribution, the birdland tag seems a bit of a misnomer—this country should probably be called the “land of lizards”. We are a veritable hot spot for herpetofauna, with more lizards found here than in any other temperate climate in the world.
New Zealand is home to two types, skinks and geckos. They are easily distinguished in that skinks blink (have eyelids that move) and are smooth and snake-like in appearance, with a narrow head. Geckos are velvety, have baggy, soft skin and a clearly defined neck, and are often excellent climbers. Instead of blinking, they have a clear membrane over their large eyes, which they can lick to keep clean. For the record, the tuatara is not a lizard at all, but a member of its own order, Rhynchocephalia (formerly Sphenodontia), which dates back to the days of dinosaurs.
New Zealand geckos can be found from one end of the country to the other—including Stewart Island—thriving in forests, scrub, grasslands, dunes, alpine areas, even under the odd woodpile or roofing tile. And though they may not be the most brightly coloured or the best climbers, scientists are continually discovering that geckos here are surpassing their overseas cousins in feats of survival and endurance. In fact, they are the longest-lived gecko population on the planet.
Geckos in New Zealand do things that no gecko should. They live for an extremely long time—more than 40 years for some wild geckos, compared with just two years for their cousins in the tropics. They don’t lay eggs; instead, female geckos retain their babies inside the uterus to protect them from cooler temperatures, and they have a slow start to life, not maturing until around seven or eight years of age for those species living in areas with very cool climates.
But the thing that really makes New Zealand geckos stand out from the crowd is the number and diversity of species in a climate normally considered too cold for their order.
New Zealand geckos have been enduring constant cycles of cold snaps and warm temperatures over the past two million years, each lasting some 100,000 years. Yet despite a couple of ice ages, continental drift, temperature changes, the more recent arrival of humans and the invariable swag of predators and pests that accompany them, New Zealand geckos still prevail throughout the mainland. To achieve this feat of survival has required the acquisition of some fabulous tricks.
Unlike any other species of gecko in the world (with the exception of one New Caledonian species), all New Zealand geckos give birth to live offspring instead of laying eggs. Keeping young inside the body ensures a far higher chance of survival than laying eggs in cool temperatures and leaving it to chance.
Alison Cree, an associate professor at the University of Otago, revealed in 1995 that common geckos at Macraes Flat in Otago were radically extending the gestation periods of their young to ensure the survival of their offspring in cooler climes.
The species Hoplodactylus maculatus is one of New Zealand’s primarily nocturnal geckos and belongs to a group of geckos usually known as common geckos. These geckos begin their pregnancies in spring and generally give birth in autumn some three to five months later. But the same species living at higher altitude just a short distance away hold onto their unborn offspring throughout winter, giving birth in spring or early summer the following year when temperatures favour survival.
The fully developed embryos simply remain in stasis within the uterus—a 14-month biennial pregnancy unheard of in geckos until Cree’s discovery.
However, when Cree and her colleagues took animals from high altitude down to a warmer temperature-controlled laboratory environment, they found that the geckos had a “normal” gestation period of around five months. This variability of pregnancy poses a bit of a problem with regard to long-held views on reptile evolution.
Tuatara, the only surviving member of the order Rhynchocephalia that thrived around 200 million years ago, have become a reference for the life-histories of Mesozoic reptiles. But Cree’s research proved that New Zealand geckos also exhibit long periods of embryonic development, low reproductive output and an extremely long lifespan—all constructs of living in a cold temperate climate. So, in the balmy climate of the Mesozoic era, tuatara ancestors may well have lived fast and died young, reversing all that is assumed of their ancient cousins.
New Zealand geckos keep breaking the records for longevity, with wild ones living beyond 40 years. Most recently, a Canterbury gecko recaptured on Motunau Island was clocked at 48 years of age. A long lifespan may be one way that our New Zealand geckos have adapted to balance their low reproductive output.
The slowly-but-surely approach to survival that is common for geckos in New Zealand is a life-strategy known as “K-selection”. K-selected species (such as humans and elephants) have a long lifespan and low reproductive rate and are slower to mature than fast-living species. R-selected species (such as mice) trade quality of offspring for quantity and seem to be at an advantage in dynamic or unstable environments.
Until very recently, the environment has been relatively stable, favouring the laconic lifestyle of the K-selected geckos. But with the rapid change brought about by humans, habitat destruction and introduced predators, geckos haven’t been able to keep up with the changes.
In New Zealand, the impact of predators on our native wildlife is well documented. Agencies, community groups and even individuals endeavour to remove the usual suspects—stoats, possums, even rats. But the diminutive house mouse is often overlooked, or just falls too far down the priority list. Removing the mouse’s predators may well have a more sinister effect on small vertebrates such as geckos.
Mice wriggle into the places in which geckos can seek refuge from other predators. Geckos, of course, are ectothermic, so in cold temperatures are too slow to escape a hungry mouse, which can literally eat them alive. And given the slow life-history and reproductive output of native geckos, it may well be decades before populations can recover from rodent predation.
Following 10 years of rat eradication on Codfish Island/Whenua Hou, Rod Hitchmough, a scientific officer with the threatened species science unit at the Department of Conservation, and a small band of researchers spent two weeks looking for green and cloudy gecko populations. They found just three individuals.
The slow life-history that makes New Zealand geckos unique may also be their undoing.
Despite their vibrant colour schemes, green geckos are almost impossible to see in the wild. I discovered this for myself while searching for jewelled geckos (Naultinus gemmeus) on Banks Peninsula at the request of the landowners.
“This is about as tough as it gets when looking for geckos,” assures Marieke Lettink, while peering through high-powered binoculars at the tops of kanuka, coprosma and other trees up to 10 m tall.
Lettink is partway through a project to compare the current distribution of jewelled geckos with historical records. It’s taking her a while to complete, not least because these geckos are very particular about their public appearances. They won’t come out to bask unless the ambient temperature is ideal for sunbathing—a degree or two over and they’ll melt back into the scrub and be impossible to find; too cold and they won’t come out at all. Consequently, Lettink is careful to plan her fieldwork around the weather forecast and won’t bother heading out unless there is likely to be at least a one-hour window in which to find geckos.
She’s certainly managed to find a few in spots where they were reported many years ago—but it hasn’t all been positive. It was particularly heartbreaking to find that one site where she’d previously found jewelled geckos had been cleared of all the scrub in which they lived. “They didn’t have a chance,” she says.
At another site near the head of Lake Forsyth, the natural habitat is gone as well. “A few years ago, this whole area was kanuka and manuka scrub,” Lettink says. “It was really good habitat, with decent numbers of jewelled geckos.”
However, both of the landowners we visited were thrilled with the thought that they might have geckos on their property—according to Lettink, most are. The first landowner saw one 15 years ago and hoped they might still be there.
She comes with us as we trudge through untouched native scrub—she’s a keen gardener, but she cherishes the native bush “out the back”—and Lettink explains how to look for the geckos.
Jewelled geckos have made the news a bit recently. Three foreigners were convicted last March for taking some from Otago Peninsula. Lettink is careful not to say much about where the geckos are found, but says that with the help of the Wildlife Enforcement Group—a collaboration of agencies from New Zealand Customs, MAF Biosecurity and the Department of Conservation—the apprehension of wildlife smugglers is getting easier and easier.
The two recent cases of gecko-smuggling and the subsequent modest prison sentences have received a lot of public and media attention and Conservation Minister Kate Wilkinson is looking into increasing the sentences for such crimes.
Lettink thinks the problem is that the geckos are up against it anyway, in terms of habitat destruction, predation and a slow-life history. Any further pressures such as poaching are just another nail in the coffin for the survival of our enigmatic lizard fauna.
New Zealand is home to two types of geckos, which have generally been described as green (Naultinus genus) and brown (Hoplodactylus genus) geckos. Genetic work may yet reveal the taxonomy to be more complicated than this, as brown gecko species have proved to be unexpectedly diverse.
Green geckos are relatively easy to distinguish due to their diurnal lifestyle and their Kermit-green colour schemes, which can include white, yellow or gold stripes, or diamonds on their backs. Green geckos live in mature native shrubland and forest and are almost totally arboreal, meaning they spend nearly all their time in the trees. While a diurnal lifestyle is unusual for geckos, green geckos can make the most of warm daytime temperatures for hunting small invertebrates and basking.
Most of the remaining 30 or so species in the Hoplodactylus genus of brown geckos are grouped as one of three types. Most are common geckos, which are largely terrestrial and nocturnal. Pacific geckos are similar in appearance and behaviour and tend to replace common geckos in the northern North Island. The remaining species are forest geckos, many of which spend a large part of their time in trees and are active from late afternoon and into the night. Others in this group live among rocks in the alpine zone.
Brown geckos can change their colour from dark to light, but the colour of green geckos is fixed.
In 1955, there were thought to be just 10 species of gecko in New Zealand. It’s difficult to get a clear answer out of any gecko scientist on the current number, but Rod Hitchmough reckons it’s safe to say at least forty. The reason for this rather imprecise description? We keep finding new ones.
“New Zealand is hugely more diverse, with regard to lizards, than other areas with a similar climate,” says Hitchmough, who has been fascinated by geckos since he was a kid.
“In Great Britain, there are just three species of native lizard, in Italy there are seven or eight. Australia has obviously got more but there’s a far greater land area, and much of it is tropical.”
So what was it about New Zealand that gave rise to so many species of gecko in such a short period of time? And how in this day and age do we keep finding more?
New Zealand gecko species are extremely cryptic—meaning there are clusters of species that all look very similar—and that can make studying them as individual species extremely difficult.
It was Hitchmough’s genetic identification work in 1986 that really started to shake up the gecko family tree. He realised early in the genetic analysis that there could be many new species of geckos, but the technology at the time couldn’t quite give him the answers he was searching for. As technology improved, so too did the ability to determine distinct gecko species. More recent molecular genetic sequencing in collaboration with Stuart Nielsen and Aaron Bauer of Villanova University in Pennsylvania, USA, using “large chunks” of DNA, has confirmed Hitchmough’s early suspicions that there were several species of geckos nested within physically similar clusters.
Species that look almost identical but are genetically distinct make it difficult for those charged with managing their population in the field. So for the past year, Hitchmough and Nielsen have been combing through gecko specimens at Te Papa to see if they can identify geckos using traditional morphometric (physical) measurements.
Their patience, and hundreds of hours spent in the backroom drawers of Te Papa, has paid off and, according to Hitchmough, they have been able to identify all known species using traditional morphometric indicators.
But you don’t need genetic analysis to identify the now-extinct Delcourt’s gecko (Hoplodactylus delcourti) or kawekaweau. It was the largest gecko species in the world, some two feet long and twice the size of others of its kind. However, there have only been a couple of sightings—the most recent in the 1870s under the bark on a tree where it was described as being as thick as a man’s wrist—and there were no physical specimens.
Then, in 1986, a stuffed, unlabelled lizard mounted on a wooden plank was hauled out of the basement of the Muséum d’Histoire Naturelle de Marseille, France. The species, 620 mm long, was unknown to science. Closer examination by Aaron Bauer confirmed that it belonged to the Hoplodactylus genus of brown forest geckos of New Zealand—a representative of a species not seen for more than a century.
It is likely to have been semi-arboreal, largely nocturnal and to have fed on fruit, insects, other lizards and, given its size, probably birds’ eggs as well.
In late 2009, the director of the museum, Anne Medard-Blondel, extracted the left femur and sent it to Bauer for genetic analysis. Bauer has since taken some dried muscle and tendon from the surface of the bone and is at present extracting and amplifying the DNA to learn more about the world’s largest gecko.
While few stones have been left unturned in gecko habitat, still more species are being discovered. It wasn’t until 1997 that the first alpine species were discovered. Black-eyed geckos have been recorded at 2200 metres above sea level, and Cascade geckos were discovered in the Sinbad Gully in Fiordland clinging to rock ledges at 1600 metres above sea level, suffering frost damage to their bodies.
But despite the number of completely new species that have recently been discovered, even more have been described as variants of common ones. And, according to Hitchmough, who has named most of them, “there are probably plenty more that have not been discovered yet”.