Nine species of moa disappeared from New Zealand in the wake of human arrival. With them went the giant Haast’s eagle and dozens of smaller bird species including adzebills, endemic geese, mergansers, harriers, teal, snipe and rails.
The landscape and ecology of this country have been spectacularly and irrevocably changed in the geological blink of an eye. According to the latest studies, moa were wiped out in less than 200 years by a population of Māori that numbered no more than 2000—not even enough to fill Auckland’s Civic Theatre.
How could this have happened? The clues lie buried at places like the Shag River mouth, and what they tell us allows us to understand not only the processes that have shaped New Zealand, but the impact humans have had on wildlife all around the world.
Scientists have a term for this phenomenon, “megafaunal extinction”, and wherever humans have ventured, it has followed. For many scientists, there is no doubt what causes it. The idea that humans entering a new ecosystem are capable of eradicating, in a short period of time, the large animals that live there is the basis of the “overkill hypothesis” first proposed by American Paul Martin in the 1960s. But ever since Martin laid out his theory, acrimonious debate has raged.
Climate change, it is often argued, played a far more pivotal role in these extinctions than direct hunting pressure. But while the major animal extinctions of Eurasia, the Americas and Australia happened so long ago that evidence for their causes is rare or absent, in New Zealand, the blood has barely dried. All of our big animals have either gone extinct or suffered major range contractions in the 750 years since the first Polynesian explorers set foot on these shores.
ACCORDING TO UNIVERSITY of Otago geneticist Nic Rawlence, New Zealand is perhaps the best place in the world to study the mechanisms of megafaunal extinction. “In other areas of the world it’s very difficult to determine whether it was humans or climate change,” he says. “At best, you can say it was a one-two whammy. But when the extinctions occurred in New Zealand, the climate was stable, so we can rule that out as a cause.”
I’m poring over a folder of scientific papers in a windowless office at the University of Otago. This is where the old New Zealand exists now—caged in screeds of jargon, reimagined in genetics labs. The documents paint a picture of beaches heaving with fur seals, sea lions and elephant seals, forests dripping with birds, skies punctured by the silhouettes of giant eagles. There are lagoons packed with waterfowl and entire mountain ranges that jabber with the screeches of millions of burrowing seabirds.
A recent article by Rawlence and his team used ancient DNA analysis to show that, prior to human settlement around 1450 AD, the Chatham Islands were the breeding site of more than 50,000 sea lions.
“You’re looking at an island archipelago that would have been filled with fur seals and sea lions,” he tells me. “You would have had islands dominated by bird life—petrels, shags, flightless rails and species of flightless duck.”
Those endemic Chatham Island species have since vanished, along with the Chatham Island sea lions, themselves a genetically unique lineage.
It seems unimaginable that a small group of people (no more than 2000 at its peak) could exterminate so many animals.
Chatham Island historian Bill Carter has also studied the extinctions and his background in the wool industry gives him an interesting perspective. He sends me a spreadsheet, of the kind used by farmers to analyse and manage a sheep flock. His model replaces breeding ewes with female sea lions and lambs with pups, factoring in birth rate, natural attrition and recruitment of young animals into the following year’s breeding stock. By plugging figures into the boxes, I can kill off as many sea lions as I like and instantly see the results.
The first revelation is that you can kill a high percentage of each year’s pups without having a big impact on overall numbers. These results are reflected on Campbell Island today, where up to half the sea-lion pups die of natural causes without adverse effect on the population as a whole. Similarly, I can get rid of a good percentage of breeding-age males. But, kill as little as five or 10 per cent breeding-age females and the population immediately starts to slump because you’re effectively killing a dependent pup, and potentially an unborn pup as well. Maintain that harvest over three, four, five years and you’re on your way to a complete population collapse.
What Carter’s model reveals is the key to the overkill hypothesis: You don’t need to eat every animal; you don’t even need to eat a quarter of them—just the critical breeders. Mathematics takes care of the remaining 50,000 individuals. Once the population is below a sustainable level, extinction is all but inevitable.
In any animal population, there is a ratio between what biologists call “effective breeders”—the animals that will pass their genes on in any given year—and the overall population. For most mammals, this ratio is surprisingly low—as little as 10 per cent of the total population are producing offspring in any one season.
Because of sea lions’ polygynous harem-based breeding strategy, where only a small fraction of breeding-age males get the chance to mate, most of the effective breeders are females. During the breeding season, these would also have been the easiest to hunt, conveniently clustered together in harems close to the hunting camps.
Sea lions are very slow breeding,” says Rawlence. “They can’t handle large amounts of hunting pressure. We know that the whole age range, from newborn pups to the largest adults, are in the midden sites [piles of shell and bones that were the remnants of hunting activity]. So they’re hunting the whole lot, they’re not being picky. If you take out a female, you’re suddenly stopping the population being replaced.”
Beaches must have swarmed with sea lions in the early days. The hunters probably thought it would be impossible to make even a dent in the colony, but within a few generations, the whole population was gone, down to the last animal.
Rawlence’s Chatham Islands research presents us with a micro-model for what happened on the New Zealand mainland some 200 years earlier. From 1280 AD onwards, Māori and the rats (kiore) and dogs (kurī) they brought with them swept across the country and deep into the heart of moa country—Canterbury and Otago. The scale of the hunt became industrial, with large processing bases established on the coast for the cooking and preservation of moa flesh, perhaps for trade with other groups further north.
It’s believed that male moa incubated the eggs and therefore would have been easy prey for hunters. Eggs were also harvested in great quantities.
For reasons that are not entirely understood, Māori burned much of the land, destroying breeding habitat and changing the ecosystem drastically. At the same time, hunters were targeting sea lions, fur seals, elephant seals, penguins and shags along the coast.
“Fur seals were breeding right up to the top of the North Island,” says Ian Smith, a University of Otago archaeologist who has extensively studied fur-seal remains from midden sites around New Zealand. “They were providing more meat for early Māori than moa, from one end of the country to the other.”
While Smith sees no evidence of massive, large-scale harvesting of seals, he believes sustenance-level human hunting intensified an already-high natural mortality rate, quickly leading to their widespread disappearance.
“What you see in the archaeological sites is that it’s predominately juvenile animals and young adults—the ones that aren’t being culled out by nature—that are being culled by people.”
Smith also points to the strong tendency of seals to return to the site they were born at as a factor in their demise. Even low levels of hunting pressure would soon cause accessible colonies to be stripped of seals.
The archaeological record stored in middens charts the disappearance of pinnipeds around our coast. Sea lions were extirpated from the mainland by around 500 years ago. Elephant seals, once a common sight on our beaches, also vanished. Fur seals retreated to remote offshore islands and inaccessible rock stacks.
Māori became increasingly dependent on fish and shellfish as the bigger animals disappeared. Where the people of earlier times had enjoyed peace and plenty, Australian science writer Tim Flannery in his seminal book The Future Eaters, scarcity and conflict now came to define Māori life in Aotearoa.
Although they probably had no way of knowing it, Māori were experiencing a pattern repeated time and time again throughout human history—the end of the golden weather, and the gathering of the storm.
THE DISAPPEARANCE OF moa and large coastal fauna was just the beginning of New Zealand’s millennium of death, by then entering its second chapter.
The first Europeans to arrive on these shores came for what was left of the New Zealand megafauna, pursuing fur seals and sea lions to their remote offshore colonies and decimating their populations.
At the same time, whaling stations along the coast quickly wiped out the southern right whales that bred there. By killing breeding females, whalers fell into the same ecological trap as early Māori. Collapse, as always, was close behind.
Just 120 years ago, the explorer Charlie Douglas was able to round up enough kākāpō from his Westland campsite to make a fine stew. Around the same time, ornithologists were collecting the last pairs of huia for museums around the world, and the laughing owl could still be heard in New Zealand forests. At least 20 bird species have become extinct in the period since colonisation.
Nic Rawlence is a geneticist with the University of Otago’s paleogenetics laboratory in the department of zoology. He’s one of a group of Dunedin-based researchers using radical new techniques to understand the effect of humans on New Zealand’s native fauna in the past 750 years.
“Working with ancient DNA is like reading Auckland’s Yellow Pages, only they’re brittle and crumbling, and you’re reading the crumbs,” he says.
Giant parrot
Ellen Mather knew something wasn’t quite right with one of the fossils she was looking at.
The PhD student at Flinders University in Adelaide was researching the fossils of eagles and hawks from Australia and New Zealand, dating back as far as 24 million years ago, to as recently as the last few hundred thousand years, not much is known about the birds, or how they relate to today’s species.
Ms Mather was given some bones for her project that were thought to belong to a large eagle. They came from St Bathans in Central Otago.
“One day I was going over them, comparing them to some specimens I had of living eagles today, such as the wedged tail eagle from Australia, and as I was comparing them I noticed that they looked really different from how eagles are supposed to look,” she said.
“The fossils lacked certain features that all eagles should have, so I realised pretty quickly that this fossil wasn’t from an eagle at all but something quite different.”
The fossil Ms Mather was examining was from the bird’s leg bone, near where it connects with the foot. In the birds she looks at, there is usually a bridge of bone across a canal, that muscle tendon goes through. “But the fossil from St Bathans, this bridge was completely absent, instead there was just two ridges on either side of the canal.” Ms Mather knew then that she wasn’t looking at an eagle.
“I went back to my supervisor, Trevor Worthy, and brought it to his attention. He took it away to try and figure out what they were – he was able to find out that they actually belonged to a giant parrot.”
That giant parrot now has an official name,(Heracles inexpectatus), and an appropriate nickname, “Squawkzilla”. It’s also made headlines around the world.
The prehistoric bird stood one metre tall and weighed in at about seven kilograms. That’s double the size of the previous record holder for the world’s largest parrot, the kākāpō.
Ms Mather said it was pretty thrilling to have been part of such a major scientific discovery. “At the time I didn’t realise that it would be so significant, but it’s exciting to have been part of that process.” Heracles inexpectatus was found in fossils dating back as many as 19 million years ago. Flinders University Associate Professor Trevor Worthy said no-one had ever discovered an extinct giant parrot anywhere until then.
“New Zealand is well known for its giant birds. Not only moa dominated avifaunas, but giant geese and adzebills shared the forest floor, while a giant eagle ruled the skies,” he said. “We have been excavating these fossil deposits for 20 years, and each year reveals new birds and other animals. While Heracles is one of the most spectacular birds we have found, no doubt there are many more unexpected species yet to be discovered in this most interesting deposit.”
Giant burrowing bat
New Zealand was once home to a giant, burrowing bat that was three times the size of the average bat today. The extinct creature, which weighed about 40g, represents the largest burrowing bat known to science, and New Zealand’s first new bat genus for more than 150 years.
Teeth and bones of the bat were recovered from sediments dated between 16 and 19 million years old, found near the old Central Otago gold and coal mining town of St Bathans.
Burrowing bats, now found only in New Zealand, are peculiar because they not only fly, but also scurry about on all fours over the forest floor, under leaf litter and along tree branches.
It has been named Vulcanops jennyworthyae, after Jenny Worthy, who was part of the team that found the fossils, and after Vulcan, the mythological Roman god of fire and volcanoes, in reference to New Zealand’s tectonic nature, but also to St Bathans’ historic Vulcan Hotel.
Its discovery, by Australian, Kiwi, United States and British scientists, has been revealed in a new study, just published in the international journal Scientific Reports.
“Burrowing bats are more closely related to bats living in South America than to others in the southwest Pacific,” explained the study’s first author, Professor Sue Hand of the University of New South Wales.
“They are related to vampire bats, ghost-faced bats, fishing and frog-eating bats, and nectar-feeding bats, and belong to a bat superfamily that once spanned the southern landmasses of Australia, New Zealand, South America and possibly Antarctica.”
Around 50 million years ago, these landmasses were connected as the last vestiges of the southern supercontinent Gondwana. At that point, global temperatures were up to 12C higher than today and Antarctica wasn’t frozen, but forested and frost-free.
With the break-up of Gondwana, cooling climates and the growth of ice-sheets in Antarctica, Australasia’s burrowing bats became isolated from their South American relatives.
“New Zealand’s burrowing bats are also renowned for their extremely broad diet,” said Hand, director of the university’s PANGEA Research Centre. They eat insects and other invertebrates such as weta and spiders, which they catch on the wing or chase by foot. And they also regularly consume fruit, flowers and nectar.
“However, Vulcanops’ specialised teeth and large size suggest it had a different diet, capable of eating even more plant food as well as small vertebrates – a diet more like some of its South American cousins.
“We don’t see this in Australasian bats today.”
The newly described species is also the latest addition to what scientists call the St Bathans Fauna.
They lived in or around a 5600sq km prehistoric Lake Manuherikia that once covered much of the South Island’s Maniototo region.
When they lived, in the early Miocene, temperatures in New Zealand were warmer than today and semitropical to warm temperate forests and ferns edged the vast palaeo-lake.
Vulcanops‘ lineage became extinct sometime after the early Miocene, as did a number of other lineages present in the “St Bathans Fauna” group, such as crocodiles, terrestrial turtles, flamingo-like palaelodids, swiftlets, and several pigeon, parrot and shorebird lineages.
Most of these were probably warm-adapted species.
The group also included the enigmatic St Bathan’s mammal, whose existence suggested that terrestrial mammals did in fact once live in Zealandia, the recently recognised “eighth continent” that today lies mostly submerged beneath the ocean.
After the middle Miocene, global climate change brought colder and drier conditions to New Zealand, with significant changes to vegetation and environments.
It was likely that this general cooling and drying trend drove overall loss in bat diversity in New Zealand, where just two bat species today comprise the entire native land mammal fauna.
All other modern land mammals in New Zealand have been introduced by people within the past 800 years.
Study co-author Associate Professor Trevor Worthy, a Kiwi scientist now based at Adelaide’s Flinders University, said the fossils showed that the prehistoric aviary that was New Zealand also included a surprising diversity of furry critters alongside the birds.
“These bats, along with land turtles and crocodiles, show that major groups of animals have been lost from New Zealand,” added another co-author, Professor Paul Scofield of Canterbury Museum.
“They show that the iconic survivors of this lost fauna – the tuataras, moas, kiwi, acanthisittid wrens, and leiopelmatid frogs – evolved in a far more complex community that hitherto thought.”
Auckland Council senior biodiversity adviser Ben Paris, better known as NZ Batman, said the discovery was “extremely exhilarating news” for the bat world in New Zealand. “I am sure it will be quite the conversation point at the upcoming New Zealand bat conference.” he said.
“It has always been an oddity of Aotearoa to have so few native land mammals, so to add this bat species to our prehistoric fauna alongside our other unique wildlife is very exciting
“This also gives us an important reminder to ‘live long and prosper’ in regard to conservation and protection of our remaining short-tailed and long-tailed bats, as they are the last of the significant bat fauna left that still provide important ecosystem services like pollination and insect control.”
The bat wasn’t the only hefty New Zealand species to be newly described by scientists, long after they were lost forever.
Researchers revealed our country once had its own black swan species that was heavier and larger than their Australian cousins, as well as a giant penguin that was as big as a grown man.
Giant swan
New Zealand was once home to some humongous birds, from the towering emu-like Moa to the largest eagle ever known to exist, the Haast’s eagle. Now researchers have confirmed the existence of yet another enormous avian, a semi-flightless mega-swan that went extinct less than two centuries after Polynesians first colonized New Zealand in the year 1280, reports New Scientist.
The find authenticates legends told by the Māori people, which speak of a mysterious bird called the Poūwa, a large swan-like creature. Though some physical evidence exists of New Zealand swans, palaeontologists have long assumed that this merely pointed toward Australian black swans (Cygnus atratus) which are known to occasionally fly across the Tasman Sea.
Researchers were able to show that the Poūwa was distinct from the Australian black swan by comparing DNA from 47 modern Australian black swans and 39 ancient swan fossils uncovered from archaeological sites around New Zealand. The analysis suggested that the mega-swan would have split from the Australian black swan about 1 to 2 million years ago.
“We think Australian black swans flew to New Zealand at this time and then evolved into a separate species — the Poūwa,” explained Nicolas Rawlence at the University of Otago, one of the researchers involved with the study.
Although the Australian black swans and the Poūwa would have shared a common origin, the two species were quite dissimilar in appearance. Using fossil remains to reconstruct what the Poūwa looked like, the research team found that these mega-swans were 20 to 30 percent heavier than modern Australian black swans, and would have weighed more than 20 pounds. They also had short, stubby wings and long legs, suggesting that they would have had difficulty flying. Short flights would have been possible, but they would have been largely flightless.
Unfortunately, being poor flyers would have left them vulnerable to human hunters, and that’s likely how these magnificent swans went extinct. Ancient trash heaps contain Poūwa remains, suggesting that the birds were commonly hunted for food. It’s also likely that their eggs were eaten by rats that were introduced by the Polynesian settlers. Slow breeding rates are also common among large animals like the mega-swan, so that could have contributed to their speedy demise as well.
“Prior to Polynesian settlement, birds in New Zealand had a pretty easy life,” said Charlotte Oskam at Murdoch University in Perth, Australia. “They were naive to terrestrial predators and would have been easy pickings for the Polynesian settlers.”
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