Tuatara – A survivor from the dinosaur age
Two hundred and twenty-five million years ago — about the time the first dinosaurs arrived on the scene — the ancestors of the tuatara were roaming the world. Now, 65 million years after the last Tyrannosaurus bit the dust, tuatara are still here, little changed from their ancient predecessors. But how much longer can they survive on their remote island homes?
Hatching is Too gentle a word to describe the birth of a tuatara. Over a period of months, the soft-shelled tuatara egg absorbs moisture from the soil, swelling up like a balloon until it is a tight-skinned capsule. Then, using its egg tooth — a sharp-pointed spike on the end of its snout — the baby tuatara punctures the shell, and its wet head literally explodes into view. Over the next few hours a series of abrupt wriggling movements will free the hatchling from the egg that has been its home for the last 12 months.
Few people have observed the hatching of a tuatara, which usually occurs in a cool, dark nest about 15 centimetres below ground. But in May of this year, 30 tuatara eggs from North Brothers Island in Cook Strait were hatched in incubators at Wellington’s Victoria University, giving us the opportunity to observe closely an event that has been happening for more than 200 million years.
Tuatara are the last surviving members of a lineage that stretches back to the Mesozoic — the beginning of the ‘Age of Reptiles’. Their ancestors witnessed not only the immense, terrifying diversity of the dinosaurs, but also geological upheavals that shuffled the continents around the globe like jigsaw pieces. Perhaps they even watched from their burrows as the earth shuddered under the impact of a giant meteorite — a disaster some scientists think occurred about 65 million years ago and led to the extinction of the dinosaurs.
Somehow the `proto-tuatara’ survived this cataclysm, hung on during the proliferation of birds and mammals, and eventually gave rise to the modern version, which survives only in New Zealand, and only just. Since humans arrived, about a thousand years ago. tuatara numbers have declined rapidly. They disappeared from the mainland a hundred years ago, and are now found only on a diminishing number of offshore refuges.
The birth in captivity of 30 healthy tuatara may mark a turning point in the long history of the animal, for these juveniles are destined to re-colonise some of the islands from which tuatara have vanished. They are the culmination of a long-term research programme that we hope will turn the tide of fate in the tuatara’s favour, away from an extinction that many have felt to be inevitable.
Tuatara have puzzled and fascinated scientists for more than a century. Since the late 1800s. naturalists have beaten a path to these shores to collect tuatara — sometimes hundreds at a time — for the world’s museums. But studying pickled specimens doesn’t save a species, and the emphasis in tuatara research is now on their behaviour and ecology.
During the last five years, teams of biologists and conservationists, working together in a project organised by Victoria University, have tried to answer basic questions about the tuatara’s reproductive biology, social behaviour and genetics. Such research is not easy. Access to the islands on which tuatara occur has long been restricted by both weather and New Zealand law. That tuatara are mainly nocturnal and have a life span that is longer than the normal scientific career does not make the job any simpler.
Besides rock-climbing skills, a good pair of sea-legs and the capacity to survive on dried foods for extended periods, all tuatara researchers require one crucial skill: the ability to catch the subjects of their study.
Tuatara emerge at dusk from their burrows and spend most of the night near the burrow entrance, waiting for a tasty meal such as a large weta or lizard to wander within striking distance. Sometimes they forage away from the burrow, perhaps on sun-warmed rocks near the high tide mark, where lizards are also searching for a meal. If the tuatara is lucky, an unwary skink may soon become supper.
Spotlit by the beam of a torch, a tuatara will do one of two things: turn tail and scuttle down the nearest burrow, or freeze like a possum. Fortunately, most choose the second option. Then, cautiously, a quick grab around the neck, just behind the powerful jaws, and the capture is successful.
Some of us have learned the hard way that a moment’s carelessness act a painful price: a bite from teeth perfected over tens of millions of years for grasping prey securely, crushing it in powerful jaws and shearing it apart even as it struggles to escape. When a tuatara clamps its sharp teeth into your bare finger. the searing pain endures until the tuatara finally decides to let go — which may be many minutes, because the tuatara has nothing if not patience (See box: its bite is worse than its bark.’)
Even if we avoid being bitten. tuatara can be very difficult to hold. Large males, the biggest as long as your arm and weighing over a kilogram, can put up a real fight, clawing and thrashing and grunting fiercely. Equally often, however, the tuatara is almost docile, displaying a stoicism that seems somehow appropriate to its antiquity.
While tuatara may be comparatively fearless at night, they are secretive and extremely wary during the day-time. Perhaps it is because the danger from predators, especially harriers circling relentlessly above many islands, is greater during the day. As a consequence, they are difficult to catch, and the risks are considerably higher. Tuatara seldom venture far from the burrow entrance during daylight hours. Usually, only the head is seen — especially if a ray of sunlight can warm it. But it’s nearly impossible to sneak up and grab the animal before it swiftly retreats to safety clown a burrow that may extend five or more metres below ground.
Often, no tuatara at all can be seen during the day. Then, the only way to find, and possibly catch, one is to go in after it. Lying face down on the fine, bare, cold soil, you slowly reach your arm into the burrow, searching blindly and gingerly for the soft skin of a tuatara — and often hoping you find nothing at all!
The word tuatara means “spiny-back” in Maori. The spines, like the skin, are surprisingly soft, much like cool, dusty linen cloth to the touch, and pose no threat. If you are lucky, your hand lands on an exposed tail or leg or, best of all, the spines and hack. Then, you press the tuatara firmly to the ground, securing it until you get a grip strong enough to pull the reluctant reptile out of the burrow. If unlucky, you find nothing, or you may just touch a tuatara as it retreats beyond your reach. Or, something may grab you. Petrels and shear-waters often use the same burrows as tuatara, and some of them have strong bites if disturbed. Worse, large centipedes with painful, poisonous stings also share burrows with birds and tuatara on islands in the Hauraki Gulf and the Bay of Plenty. Or, a large tuatara may express its displeasure with a sharp, unrelenting bite.
Bitten or not, a visit to a tuatara island is the experience of a lifetime. Few people ever get the opportunity, though, because tuatara have been fully protected since 1895, and permits to land on their home turf are not given lightly.
But what astonishing places these islands are! Many, like Stephens Island in Cook Strait or Tawhiti Rahi and Aorangi Islands in the Poor Knights, rise straight up from the sea like stark, primeval fortresses. Cliffs a hundred metres high are topped with thick carpets of wind-shaped scrub: taupata, ngaio, or mahoe. In spring, the northern islands are red with flowering pohutukawa and, on a few islands, the glorious Poor Knights lily.
The surrounding seas are often turbulent, and landing a dinghy can be both difficult and dangerous; on many of these islands there is no such thing as a beach. A research team of four to six people must be shuttled ashore, the dinghy stacked high above the gunwales with supplies. There’s no going back for forgotten gear, so everything required for a week’s work has to be remembered and included: food, tents, personal gear, scientific supplies, and plenty of torches and batteries, because most work is done at night. Often, all our drinking water has to be taken with us, too.
Once ashore, several hours are spent drying out wave-swamped gear, pitching tents in tiny openings at the margin of the scrub, and preparing gear for the first night’s work. In daylight, tuatara islands often seem strangely quiet, with only a few parakeets or bellbirds for company, so the first few hours ashore are a peaceful interlude before the real work — and excitement — begins.
Signs of life are everywhere. The soil is usually bare from continual digging and trampling by birds and tuatara, and is riddled with burrows. But the scrub is thick, and we often have to crawl under or through the brittle, scratching branches. The combination of forest, soil and bird droppings gives the area a distinctive, pungent bouquet. Particularly ripe is the smell of a blue penguin nest, full of decaying faeces and the remnants of fish and squid regurgitated by the parents as food for the young.
As night approaches, there is an explosion of life. Most tuatara islands are free from mammals, and thus teem with birds, lizards, weta, and beetles. From August to November, when seabirds return for breeding, the night-time cacophony of tens of thousands of these creatures creates a wall of noise. Sleep is almost impossible, not only because of the din, but because petrels crash-land on your tent with monotonous — but nevertheless startling — regularity. Then, just as you manage to doze off with the approaching dawn, an army of aucous penguins marches past your tent on their way to the sea!
Walking around these islands at night can be unnerving, as some seabirds seem attracted to the headlamps we wear for illumination. Every few steps a surprised bird bounces off an equally surprised scientist. On islands in the Hauraki Gulf, the beaches are alive with lizards, too — black Suter’s skink and the brown, velvety Duvaucel’s gecko, the largest surviving gecko in New Zealand. Under the low forest canopy on several islands, giant weta prowl through the vegetation, careful to stay out of the way of tuatara.
Tuatara islands differ dramatically from the New Zealand that humans have created with their cities, highways, farms, orchards, exotic forests, rabbits and hedgehogs. The forests are silent because the birds that once teemed in them have been killed by rats, cats, and stoats; the trees themselves dying because of possums brought from Australia. To visit a tuatara island is to travel backwards in time for a thousand years, or a million, or ten million — to a time when most of New Zealand shared the extraordinary biological diversity now found only on those few offshore islands where introduced mammals are absent.
Some species are gone forever, of course: moa, sea eagles, the giant gecko. But on tuatara islands, life is super-abundant. Seabirds fertilise the soil with their droppings, producing the rich plant communities that in turn provide food for insects, lizards, forest birds, and, at the top of the food chain, tuatara.
On Stephens Island, in Cook Strait, the average tuatara weighs 400-500 grams, and in some places as many as 2000 tuatara share one hectare of forest — almost a tonne of tuatara per hectare. Even in poorer habitats, numbers are as high as 500 per hectare. Such numbers are possible only because the soil, enriched by the tens of thousands of fairy prions that return to Stephens each year to breed, supports a diverse biological community that tuatara see as an enormous buffet.
Anything that moves is fair game to a tuatara: earthworms, beetles, lizards (seven species on Stephens Island), frogs, weta, injured or juvenile prions, and even, as our colleague Mary McIntyre discovered, young tuatara. Mary was studying hatchling and juvenile tuatara on Stephens Island. The behaviour and ecology of young tuatara have long been a mystery, because they are seen so infrequently, even on islands where adult numbers are high. To discover where the young hide, Mary taped small spools of cotton thread to the tails of a few juveniles and tied the ends of the threads to nearby plants. As the juvenile moved about, the thread unwound behind it, leaving a complete track of all its movements. Twice daily, she would begin at the tied end and follow each animal, mapping its entire path, finally clipping off the unwound thread when she caught up to the young one, and starting the process over again.
Day after day, Mary followed juvenile tuatara this way, showing that they sought shelter from the hot summer sun under small rocks in open areas, under thick clumps of grass, even under the leaves of thistles, and along the forest margin. Unexpectedly, however, they were most likely to move about in the daytime, despite the danger of overheating or drying out.
The reason soon became apparent: “I followed the thread trail of a year-old tuatara that disappeared under a rock in the lighthouse keeper’s sheep pasture. Gently lifting the rock to find the juvenile, I was shocked to see the thread disappearing into the mouth of a large adult male along with the tip of the tail of the young on
Mary concluded that adult tuatara are probably an important predator of baby tuatara, which may explain why juveniles are most active in the daytime, seeking shelter at night when adults are foraging for food.
Studies of tuatara on Stephens Island began in earnest over 40 years ago. Bill Dawbin, then a lecturer at Victoria University specialising in whale biology, visited Stephens with an American herpetologist. Dawbin was captivated by what he saw, and returned repeatedly between 1949 and 1981 with teams of field workers who marked and measured hundreds of tuatara each trip. The capture and measurement of the same individuals over a 30-year period allowed
Dawbin and others to confirm that tuatara are extremely slow growing, reaching reproductive maturity between ages 10-15, continuing to grow until age 30, and living for at least 6070 years. Other studies during the 1970s and early 1980s by Don Newman and Geoff Walls, both now with the Department of Conservation, provided important additional information about numbers, food, and territory size of tuatara on Stephens.
A new set of studies began in 1985, when Mike Thompson, a tall, gregarious Australian, arrived at Victoria University. An expert in the nesting ecology and egg incubation of turtles, Mike quickly convinced us that similar knowledge for tuatara was essential for their preservation.
The first problem was finding tuatara nests. Previous reports of nesting were scarce, at best anecdotes that required confirmation. Even the timing of nesting was uncertain. Don Newman had taken X-rays of tuatara, indicating that eggshell formation occurred as early as September, but some females were obviously still carrying eggs as late as December. Mike began intensive searches for nesting females in September 1985, continuing until the end of November. None was found.
The next year, Mike assembled a small army of volunteers (including one of us — Alison Cree) to conduct nightly patrols for nesting females on Stephens Island from September until December. Team members searched either for females digging burrows or for ‘scrapes’, evidence of such digging. For weeks, we followed numerous female tuatara daily, recording their every movement, but finding no evidence of nesting.
At last, in November 1986, the action we had long anticipated was discovered. Several females that had not moved more than a few metres from their home burrows since September suddenly sprinted several hundred metres in a few nights, disappearing down cliff faces too steep for us to follow. Later that month, other nest sites were found, but in a surprising location. In the previous year, searches for nesting females had focused on the small patches of remnant forest on top of the island. In 1986, Mike established a search pattern that covered not only the forest areas, but also the expanses of pasture used for the past century by lighthouse keepers to raise sheep. (Most of Stephens Island was cleared of forest last century, making it the least natural of any tuatara island.)
On a warm night in November 1986, Mike stumbled on a nesting tuatara that was within sight of the front window of the field station. A rapid search revealed that females were nesting in rookeries all over the sheep pasture. Months of despondency changed to instant elation, and we immediately began marking the locations of all nest sites, using metre-high stakes topped with reflective tape. Lou Guillette, a visiting scientist from the University of Florida, couldn’t believe his eyes on arriving at Stephens a few days later: “The hillsides were transformed at night — the twinkling stakes in our headlamp beams looked like a road construction site. I’d read that almost nothing was known about tuatara nesting, yet here it was happening en masse!”
It turns out that the nesting behaviour of tuatara can be easily observed, once you know where to look. Apart from sea turtles that come ashore in large numbers to nest on sandy beaches, most reptiles are very secretive during egg-laying. Female tuatara, however, have prolonged, highly visible and surprisingly active nesting behaviour. Mike Thompson describes it: “They come to nesting areas from hundreds of metres away, spend several days or even weeks digging a shallow nest hole, and then lay about ten eggs in it. Once the eggs are laid, the female fills the nest hole with soil and grass, returning to it nightly for up to a week after laying. Females even appear to guard the nest, presumably from other females, who have been seen digging up other females’ nest holes to use for their own eggs.”
For the next three years, Mike and Alison returned monthly to check on the development of nests and to study the reproductive cycle of adult tuatara. Some of the animals studied were, in fact, the same animals marked decades earlier by Bill Dawbin and his teams. Many had not grown in the intervening period and were probably at least 60-70 years old. Scientists of the future will check on the survival of these well-known animals. and when such studies are made, we may discover that a few of the biggest, oldest tuatara on Stephens Island watched Captain Cook sail by in 1769.
To hold a tuatara is to be forced, inevitably, to contemplate history. Not only the history of that individual, but the history of its ancestors in New Zealand and even before. when New Zealand was part of the ancient continent of Gondwanaland. For tuatara are the great survivors in New Zealand. Their ancestors, the first sphenodontidans (a name meaning ‘wedge tooth’), shared virtually all continents with dinosaurs. They appear as fossils from North America, Europe, England and Africa, from 225 million years ago until about 120 million years ago. Most are smaller than tuatara, and they would not have threatened the reptilian giants with whom they shared the earth. They probably survived in much the same way as today: by being nocturnal, or at least cautious and secretive.
But eventually, like the dinosaurs, they, too, became extinct. Everywhere except in New Zealand, that is. About 80 million years ago New Zealand broke free from Gondwanaland, not long before the last of the dinosaurs disappeared. Mammals then began their spectacular evolutionary rise, dominating all continents except Antarctica ever since.
For reasons unknown, the sample of animals stranded on New Zealand as it drifted northward through the Pacific, away from Antarctica and Australia, differed (or came to differ) from those that survived or prospered on the other southern continents. Most importantly, no terrestrial mammals survived in New Zealand. Nor did land snakes or tortoises. But the ancestors of tuatara did, and in the absence of mammals they thrived. Bones of tuatara from coastal dunes show that tuatara were abundant throughout the North and South Islands until the arrival of humans.
New Zealand is famous for its giant extinct birds, but research in the past decade shows that pre-human New Zealand was as much the land of reptiles as of birds. Most spectacular was the giant gecko, Hoplodactylus delcourti, as large as a possum and possibly the taniwha of Maori legend. (See Geonews.)This animal may have stalked the forests of New Zealand and been an important predator of birds and reptiles. The rich lizard faunas of many offshore islands and a few mainland locations show that lizards can be extraordinarily abundant. In some sites today, numbers are as high as 4000 per hectare, even with mammalian predators. They could have been even higher a millennium ago.
Even native frogs have been underestimated in importance. Now, only three small species survive, almost exclusively in the North Island, and two of these are extremely rare. But a thousand years ago, twice as many species of native frogs occurred throughout the country, and one of these was the size of a bull frog.
So, when the first Polynesians stepped ashore in New Zealand a thousand years ago, they would have confronted a relict fauna from the Age of Reptiles. Their first meal of New Zealand food was as likely to have been tuatara as birds or shellfish. And from then until today, the effects of humans and their mammalian followers — rats, dogs, pigs, goats, cats, stoats — were as disastrous for reptiles as for birds, frogs, wetas, and virtually all other ancient New Zealanders.
But the tuatara has survived. Just as the ancestors of tuatara escaped extinction through the good fortune of finding a last refuge in New Zealand — that “ultimate storehouse for discontinued zoological models,” as Time magazine put it — so the tuatara itself has survived by finding refuge on a few coastal islands, some barely the size of a tennis court.
During hundreds of years of Maori occupation of New Zealand, tuatara numbers probably declined steadily, but when Europeans arrived, tuatara were still found on both main islands. (None has ever been known from Stewart Island.) Maori hunting seabirds must have known tuatara all too well— a hand thrust down a bird burrow in search of a meal might frequently have been withdrawn with a tuatara attached instead. The Maori had many names for the species, including ruatara, tuatete, and narara or ngarara, in addition to tuatara. And while it may have been an important food item for some tribes, the tuatara, like the lizard, was regarded with respect, as an embodiment of supernatural powers, sometimes evil.
No member of Captain Cook’s expeditions records having seen tuatara, although during Cook’s third expedition two Maori boys described “a monstrous animal of the lizard kind” that may have been a reference to it. Early Europeans called them `guana’, ‘the great fringed lizard’, and ‘the tuatara lizard’. It was a full 50 years after Captain Cook’s first landing before the species came to the attention of European scientists. Even then, it was another half century before its full scientific importance as a ‘living fossil’ was appreciated. Since recognition of its importance in 1867, the tuatara has been the subject of at least 1500 scientific papers.
Nonetheless, much remains to be learned about tuatara, especially its requirements for survival. On only seven islands are tuatara populations reasonably secure (See ‘The fight for survival.’) As with many other New Zealand species that now survive only on offshore islands, the tuatara’s future may be precarious for many decades. But we are betting that tuatara pull through, just as they have for tens of millions of years. Fortunately, the respect, perhaps awe, which the later Maori accorded tuatara is shared by increasing numbers of modern New Zealanders, whatever their origins. Even more respect, combined with vigilant conservation care, is required to ensure that the tuatara has a chance for a future as long as its past.