There are two types of lizard in New Zealand: skinks and geckos. Those most commonly seen are small and dull-coloured. But this belies some unique adaptations to a temperate climate, and a great diversity – new species are being discovered all the time.
Skinks and geckos
New Zealand has two types of land reptile – lizards and the tuatara. Lizards are a diverse group worldwide, but in New Zealand there are only two families – skinks (Scincidae) and geckos (Gekkonidae). New Zealand skink and gecko families each have two genera, in each of which there are many species. Three genera are found nowhere else, while species in the fourth genus are also found on Norfolk and Lord Howe islands. Although these islands are Australian territories, their plants and animals are closely related to those in New Zealand.
It is not certain how many skink and gecko species there are in New Zealand. The last review, published in 1994, listed 62, many of which were yet to be named. Since then, species have been discovered faster than taxonomists can describe and name them. There are probably at least 80 species that are endemic (occur only in New Zealand). New Zealand has more lizard species relative to its land area than many other countries. It can be difficult to identify them, as the most up-to-date field guide, New Zealand frogs and reptiles (1996), does not include all known species.
There is only one introduced lizard species – the rainbow skink (Lampropholis delicata), which probably arrived from Australia in a ship’s cargo.
Skinks and geckos are easily distinguished:
• Skinks are smooth-skinned, sleek and shiny, with small legs. They have small eyes and can blink.
• Geckos have scaly skin that feels silky and looks one size too large, and stout legs. Their eyes are large and cannot blink.
Most of New Zealand’s skinks and geckos are small, and the few species people usually see are dull-coloured. Until recently these lizards attracted little attention from zoologists.
New Zealand lizards are unusual in that only one, the egg-laying skink, lays eggs. The others are viviparous – they give birth to live young. The eggs hatch in the female’s oviduct before the youngsters are born. Common skinks (Oligosoma nigriplantare) and possibly other species grow a placenta, and the developing embryo is nourished by its mother. Vivipary is thought to be
an adaptation to New Zealand’s cooling climate during the ice ages – most other viviparous lizards occur in colder regions of the world.
New Zealand skinks and geckos produce fewer young than most species overseas. New Zealand geckos normally have two young each time they breed. Most breed once a year, but Duvaucel’s gecko (Hoplodactylus duvaucelii) and the Macraes (Central Otago) gecko (H. maculatus Macraes form) breed every second year. A Macraes gecko’s pregnancy lasts 14 months, perhaps because cool temperatures slow the foetus’s development. Most other New Zealand geckos mate in spring or summer and give birth in autumn or winter. Skinks usually have between two and five young at yearly intervals.
New Zealand lizards have unusually long lives. One Duvaucel’s gecko lived for at least 36 years, and many of the smaller common geckos live more than 20 years. Skinks do not live as long – the largest live about 10 years.
Origins and diversity
Before people and mammalian predators arrived in New Zealand, lizards were widespread and abundant. They still occupy virtually all habitats, from intertidal rocks to alpine bluffs, and from semi-arid Central Otago to rainforests in Westland. Lizards live on the Three Kings and Chatham islands, but noNeighbot on the subtropical Kermadecs or the cold subantarctic islands.
In some parts of inland Otago up to eight lizard species occur together: a local form of the common gecko, the jewelled gecko (Naultinus gemmeus), and six species of skink. Also in Otago, up to three large skink species may be found living near each other, but not in the same habitats. These are the grand skink (Oligosoma grande) on rocky outcrops, the green skink (O. chloronoton) in moist, well-vegetated areas, and either the Otago skink (O. otagense) on bluffs, or the scree skink (O. waimatense) on scree slopes. Up to three smaller skink species may also be present, each with its own particular habitat requirements.
Kawekaweau in Marseille
Māori call reptiles ngārara – a term that includes tuatara, lizards, and giant reptiles from tradition. One story tells of a giant forest lizard, the kawekaweau. In the Natural History Museum in Marseille, France, there is an unlabelled, stuffed lizard that could be this creature. It belongs to the genus Hoplodactylus, which occurs only in New Zealand. Where it was found and how it ended up in a French museum is unknown. In 1870 an Urewera chief killed a large lizard that resembled the Marseille specimen.
The geckos belong to the subfamily Diplodactylinae, a primitive group found only in Australia, New Caledonia and New Zealand. Other, modern geckos have colonised many remote Pacific islands, but Diplodactylids are less able to survive long ocean voyages aboard flotsam. Significant differences between New Zealand and Australian Diplodactylids suggest that geckos may have been in New Zealand for tens of millions of years, perhaps since it broke away from the Gondwana supercontinent, about 85 million years ago.
The diversity of skinks and genetic differences between species indicates that they must also have been in New Zealand for many millions of years. Just how they got there and where they came from is still debated. Some researchers suggest that skinks arrived from New Caledonia more than 40 million years ago, when the sea level was lower and it may have been possible to island-hop south. Others think that skinks and geckos came to New Zealand during the last 20 million years. Further research is likely to clarify this.
Many new lizard species have been recognised using DNA analysis, which has shown that what was once considered a single species is in fact several species. For example, the gecko previously classified as Hoplodactylus maculatus is now known to consist of nine species. Their geographically separated forms have evolved from a common ancestor. In another case, one previously recognised subspecies of skink, Oligosoma nigriplantare maccanni, was reclassified as four unique species, each with a specific habitat preference that stops them from interbreeding.
Mammal predators pose the biggest threat to native reptiles. Kiore or Pacific rats (Rattus exulans) arrived with Polynesians about 1250–1300 AD and
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caused the extinction of some lizards on the mainland and on the smaller islands. In the late 1700s and early 1800s, European rats, mustelids (ferrets,stoats and weasels) and cats caused another wave of local extinctions.
The past and current distributions of Duvaucel’s gecko show the impact of predators. Before predators arrived, the geckos occured on the North and South islands, from Northland to at least as far south as Otago. Today they survive only on a few predator-free islands from Cook Strait northwards.
At least three lizard species have become extinct since people first discovered New Zealand. Eight species have become extinct on the mainland but survive on islands where there are few predators. Those surviving on the mainland are less common than they once were.
Large, nocturnal species are most likely to become extinct, as mammalian predators usually hunt at night. For example, all large species in the genus Cyclodina are nocturnal. Large species of Cyclodina are all but restricted to rat-free islands, and small species still occur on the North Island. All were once widespread across the North Island. Even large, day-active lizards are vulnerable to predators and today occur only in small, widely separated populations – just a portion of their original range.
Almost half of New Zealand’s reptiles are threatened or endangered. It is now illegal to handle or keep in captivity any native lizard without a permit from the Department of Conservation. Some, such as the spotted skink (Oligosoma lineoocellatum), are still widespread, although their numbers are probably dwindling. Others are endangered, including the Otago and grand skinks, two of the country’s largest (up to 30 centimetres long). They live in mountain tussocklands in Central Otago, but occupy only one-tenth of their original range. The reason for this is unclear. They may have fallen prey to cats, especially in winter, when cats are hungry and lizards slow. Natural fires and agricultural development are also threats. Research is under way to manage these hazards and help these species recover.
Until recently there have been few attempts to save endangered or rare reptiles from extinction. The eradication of
rats from islands such as the Mercury Islands off Coromandel Peninsula has brought new hope for some lizard species.