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Extinctions

by  Richard Holdaway

Extinction is the final and irrevocable end of a species, and the fate of most living things throughout the earth’s history. Many of New Zealand’s native animals have been lost since people arrived – including the hefty moa and the lovely huia, and a host of less familiar species. We may just be able to save the takahē, the saddleback and other creatures that are hovering on the brink.


The concept of extinction

What is extinction?

Extinction is the permanent end to the existence of a species. Through the vast expanse of geological time, extinction has been the fate of most kinds of living things on earth. The background rate of extinction has been more or less constant at about one species per million each year. New species arise at about the same rate. From time to time a mass extinction event occurs.

Extirpation

Extirpation means the loss of a species in a local area. For example, the tuatara (a lizard-like reptile) has been extirpated from New Zealand’s North and South islands, but small populations still survive on island sanctuaries.

Ideas about extinction

The concept of extinction, at least in Western cultures, was accepted only about 200 years ago. Before that, it was assumed that each species was permanent and had existed for as long as the earth had. But as more fossils of unusual animals were unearthed, the idea that groups of these animals were still living in remote areas became untenable. By 1800 AD it was realised there were simply not enough places left for large, extinct species such as mammoth and giant sloth to hide.

Investigating extinction: Georges Cuvier

Naturalist Georges Cuvier, working in Paris around the beginning of the 19th century, realised that many fossils were of forms that no longer existed. The fossil record showed that whole groups of animals had become extinct in Europe and elsewhere. Cuvier developed methods to reconstruct the appearance of extinct species, by comparing the fossils or bones of extinct species with related existing species.

Richard Owen and New Zealand’s moa

In the late 1830s, Richard Owen in England made the British public aware of extinction, and extinct animals. On the basis of a single piece of bone sent from New Zealand, prompted by John Rule, the bone's owner, Owen deduced that huge birds related to ostriches once lived there. This idea was much publicised, and Owen’s reputation was partly founded on his series of studies of these birds, named moa by Māori. Owen named them Dinornis, meaning strange or striking bird.

Moa become extinct

Meanwhile, no living moa were found. This lack of live moa in New Zealand, like that of live mammoths and dinosaurs anywhere in the world, established the reality of extinction. Their bones or fossils remained, but the living creatures are gone. Owen’s widely distributed pamphlet prompted colonists in New Zealand to send a steady stream of bones to England. New Zealand was one of the first places where debate over extinction was part of public and scientific life.


Pre-human extinction events

Extinction events

There have been times in the earth’s history when the rate of extinctions was particularly high. This is called an extinction event – a period which sees the wholesale extinction of species of animals or plants over large areas, in the sea, or on land, or both. It can happen on a regional or global scale.

Some extinction events have involved almost all organisms living at the time. Five major worldwide events over the last 550 million years have been recognised.

Permian–Triassic extinction: the third extinction

One of the largest extinction events, called the third extinction, happened at the end of the Permian period, about 250 million years ago. Over 94% of the species recognised from fossils as being alive before the event became extinct at this time.

Cretaceous–Tertiary extinction: the fifth extinction

The extinction of the large dinosaurs worldwide (including those in New Zealand) occurred at the end of the Cretaceous period, 65 million years ago. This is the most widely known extinction event, although it was far less catastrophic than the one at the end of the Permian period. The Cretaceous–Tertiary extinction is also called the fifth extinction.

Loss of diversity in New Zealand

In New Zealand, plant and animal diversity was probably at its greatest during the Miocene period, around 15 million years ago. As in Australia today, eucalypts, she-oaks, and Wollemi pines grew. There were crocodiles, large bats that resembled fruit bats, and a bigger range of ducks and geese than in later times.

A major cooling phase around 2.4 million years ago led to changes in the fauna and flora worldwide. On continents, plants and animals could gradually move closer to the equator as the higher latitudes cooled. But New Zealand did not have such a latitudinal range, so it lost some of its subtropical species around that time.

Climate change

Climate change is always accompanied by changes in the distribution of plants. In New Zealand, changes to the forests undoubtedly affected the distribution and abundance of bird species such as moa and the giant Haast’s eagle (Aquila moorei). For example, the eagle and two large moa (the stout-legged moa Euryapteryx gravis, and the heavy-footed moa Pachyornis elephantopus) were common on the West Coast and in north-west Nelson during the most recent (Ōtira) glaciation, 20,000 years ago. Fifteen thousand years ago, as the climate warmed and multi-storeyed forest returned, these species vanished west of the main divide (the line of highest peaks in the Southern Alps). They were still plentiful in their preferred habitat of forest–shrubland mosaic to the east, right up to the time of Polynesian settlement around 1250–1300 AD.


Extinctions in the human era

Causes: ice ages

Within the human era (around the last 200,000 years) an extinction wave, often referred to as the sixth extinction, has been sweeping around the world. On each landmass the first group of animals affected has been the megafauna – the largest mammals and birds of each landmass.

The extinction of the large mammals of North and South America was recognised in the early 19th century. For many years it was thought that the inhospitable ice-age climate caused their extinction – even though it happened at a time when the climate was improving, at the end of the last ice age in the late Pleistocene period (around 14,000 years ago).

… or hunting?

In the 1960s American paleontologist Paul Martin suggested that human hunting was a primary cause for the major extinctions 10,000–12,000 years ago in America. Since then, this ‘Pleistocene overkill’ hypothesis has remained controversial, but it is supported by an increasing amount of evidence, including data from improved radiocarbon dating methods. This has shown that a wave of regional extinctions took less than 1,000 years to cross North America, with megafauna disappearing from a region soon after humans first arrived there.

Among the species lost from North America were mammoths, mastodons and giant sloths, along with the American horse, camel, lion, cheetah and sabre-cat.

Human impact in Australia

The first humans to settle beyond Africa and Asia were those who reached Australia (via Indonesia) between 50,000 and 40,000 years ago. The following few centuries or millennia saw the end of Australia’s giant mammals and birds. Huge cow-like marsupials and a 500-kilogram relative of the goose, nicknamed ‘the demon duck of doom’, vanished as hunting and fire transformed the large continent.

Remaining megafauna

Most of the world’s remaining large wild land animals – such as elephants, tigers and giraffes – are on the continents of Africa and Asia, where they co-evolved with hominids (members of the human family). These animals evolved defence strategies to keep pace with early humans’ methods and tools for hunting. This meant that the contest between predator and prey was relatively even. In lands colonised after humans reached their modern form, such as Australia, the Americas, Oceania (including New Zealand), hunters encountered animals that had evolved free of human predation. This prey could be hunted more quickly than it could replace its numbers by reproduction.

Animals arriving with humans

As they migrated around the globe, people took animals with them to new land masses. On oceanic islands where there were few mammal predators or browsers, the new species have wiped out native species, or made radical changes to the environment by altering the vegetation.

New Zealand: the last wilderness

New Zealand was the last large habitable land mass to be colonised by humans, and is the most recent to experience an extinction event. It was the last primeval wilderness on the planet. Extinctions of species such as moa and Haast’s eagle began with the arrival of humans and kiore (Pacific rats), and are still happening. Most evidence points to a first human arrival date between 1250 and 1300 AD. It has been suggested that kiore might have reached New Zealand much earlier, around 2,000 years ago – with transitory human visitors.


New Zealand extinctions since human arrival

Migrating to New Zealand around 1250–1300, Polynesians brought kiore (the Pacific rat), which wiped out some smaller species of bird, as well as frogs and lizards.

Europeans came from the late 18th century, bringing Norway rats and ship rats, cats, stoats, weasels and ferrets. Like the kiore, these predators could reproduce rapidly and disperse widely. They vacuumed up the smaller prey (and continue to do so), starting with whatever was easiest to catch – frogs, lizards, invertebrates and small ground-nesting birds. But the new arrivals could also kill larger prey, and some were good climbers and not so afraid of water. This meant that species that had survived attack by kiore were now at risk.

Humans hunted large, conspicuous prey – seals, moa and other large birds – as long as they could be found. This resulted in the first human-caused extinctions of New Zealand species.

Why so many bird extinctions?

New Zealand birds evolved in isolation over millions of years. Unlike elsewhere, there were no land mammals such as bears, badgers, lions or goats. Free from attack and competition from mammals, many birds became ground-dwellers. They were therefore natural prey for humans and the predators they brought, and vulnerable to land clearance.

Discovering extinct birds

In New Zealand, European settlers noticed the evidence for the extinction of the megafauna – moa and other large birds – from around the late 1830s. Moa bones belonging to a number of moa species were found in middens (ancient rubbish sites), swamps and caves. The remains of other species, including large extinct geese, adzebills, and the giant Haast’s eagle, were also discovered before the end of the 19th century.

Just how many smaller birds had become extinct was not realised until after 1990, when the food remains of the extinct laughing owl were discovered and analysed. Beneath the owl’s former roosts in sheltered caves were layers of bones of their prey, piled up over centuries. These bones were evidence of the former abundance of birds such as saddlebacks, now killed off on the mainland, and surviving only on predator-free islands.

Returned to the soil

At some southern South Island archaeological sites where moa bones were found in the 19th century, the bones were so abundant that they were carted away and ground up for fertiliser.

Loss of creatures large and small

The extinctions in New Zealand have been unusual because small species died out at the same time as the megafauna (large birds in this case). Now most of the large species are gone, and small birds continue to be threatened and lost. Indeed, the New Zealand extinctions have aspects of both the continental extinctions (involving mainly large species), and of island extinctions (where small species were the main casualties).

Overall losses

Over a period of 750 years New Zealand’s vertebrate fauna has been nearly halved, and there have been uncounted losses of populations and species of invertebrates.

The list of New Zealand species known to have become extinct since human settlement includes one bat, at least 51 birds, three frogs, three lizards, one freshwater fish, four plant species, and a number of invertebrates. Of these, 21 bird species, the bat, fish and two lizards survived 500 years of human and kiore predation. Although often severely depleted they appeared in European drawings, written records and museum collections. But as new, effective predators arrived, they slipped into extinction.

Back from the dead

So-called zombie species – those which might otherwise be extinct – have survived because humans protect them from introduced predators. They include species that no longer have natural populations (such as the kākāpō), and those maintained in captivity or in part of their original range (such as the South Island takahē).

Plants and fungi have not escaped – several are extinct, and over 100 plant species are classified as critical or endangered. Some birds are still declining: the bush wren, South Island snipe and South Island kōkako were last seen alive in the 1960s.

Remnant bird populations

Other bird species have been drastically reduced. The South Island takahē was once widespread in places such as North Canterbury’s plains and foothills. Loss of habitat, along with hunting, reduced it to a tiny remnant in Fiordland. The only North Island takahē seen by Europeans was carried down from the Ruahine or Tararua ranges in 1894. More seabird than land bird species have survived, as many were on offshore islands.


Extinction of large birds

The first birds to become extinct, within a century or two after human arrival, were the largest – all species of moa, both species of goose, and both adzebill species. Being flightless, all would have been quite easy to hunt and catch, yielding large quantities of meat. Their slow breeding rate meant they were lost faster than they could be replaced.

Big geese and adzebills

The South Island goose was three times bigger than the introduced Canada goose, weighing 18 kilograms and standing a metre tall; the North Island goose was rather smaller. They grazed in open country and were flightless.

The stocky North and South Island adzebills were similar to the geese in weight, and 80 centimetres tall. Arising from the same stock as rails, they have no close living relatives. They were well-equipped predators, with strong feet and a bill the width of their head, tapering to a point. They might have eaten ground-nesting birds including seabirds and ducks, as well as lizards, tuatara and invertebrates.

Six ducks

Six ducks are now extinct, five of them within about 200 years of Polynesian settlement. They included a musk duck, a stiff-tailed duck and the stocky Finsch’s duck, which may have been flightless.

The sixth species was a merganser – a fish-eating duck with a long, thin, serrated bill, unlike typical ducks. The southern merganser, extinct on New Zealand’s main islands by the 1500s, had an isolated population on the subantarctic Auckland Islands. These islands were free of mammalian predators until pigs, cats and mice were introduced during the 19th century. The last known southern merganser was shot for Governor Lord Ranfurly’s collection in 1902.

Flightless rails

Six flightless rails and two coots became extinct. Weighing over four kilograms, the North Island takahē or moho was the world’s largest rail – taller and heavier than the South Island takahē but less rotund. It was seen by few Europeans, and surveyor Morgan Carkeek brought one out from the Ruahine or Tararua ranges in 1894. It was identified by older Māori who still remembered them, and elders of the Muaūpoko tribe came to pay their respects.


Smaller birds, reptiles, frogs, fish, plants

Whereas larger birds were most vulnerable to human hunting, smaller birds, bats, reptiles and fish were vulnerable to kiore, other rats and larger predators. The main threats facing plants have been land clearance and browsing mammals.

New Zealand wrens

The smallest birds to become extinct were four species of the distinctive New Zealand wren (not related to northern hemisphere wrens). Three species were flightless, and would have scurried around in forest and scrub like two-legged mice.

Wrens were vulnerable to kiore (Pacific rats). Two species – the long-bill wren and the stout-legged wren – disappeared. They disappeared long before European settlers arrived.

The Stephens Island wren, once found all over New Zealand, had a last stronghold on kiore-free Stephens Island. It was safe until cats arrived and the forest was removed in the 1890s, and was last seen in 1895.

The bush wren or mātuhi (a 16-gram bird that was able to fly) gradually dwindled in mainland forests. It was last seen at Nelson Lakes in 1968. Rats from a boat invaded its last island refuge, Big South Cape Island (Taukihepa) in 1962. These rats also caused the extinction of the greater short-tailed bat and the South Island snipe.

Piopio

Both the North and South island species of piopio were plentiful when European settlers arrived, but were extinct by the early 20th century. Related to the Australian whistler group, piopio were skilled songsters that could mimic other species. They were known as ‘native thrush’ as they resembled thrushes, with brown upper parts and (in the South Island bird) flecked under parts.

Huia

The huia has come to symbolise the tragedy of New Zealand extinctions. Greatly significant to Māori, this glossy black bird had white-tipped tail feathers and orange-red wattles, and a deep, melodious call. The female’s bill was long, slender and down-curved, while the male’s was shorter and pick-like. Huia did not fly often. Usually they sprang about on their long legs.

Māori valued their tail feathers, worn on special occasions by people of high rank, and stored in carved wooden boxes.

The rapid decline of huia was noted after new predatory mammals were introduced in the 1890s. The last (unconfirmed) sightings of this mystical bird were in the 1920s.

Greater short-tailed bat

One of New Zealand’s three bat species gradually disappeared on the main islands, surviving on Big South Cape Island (near Stewart Island) until it was invaded by rats in the 1960s.

Reptiles

New Zealand had many skinks and geckos, as well as two species of tuatara. An unknown number are extinct – their skeletons are less durable or identifiable than those of birds.

The world’s largest known gecko, kawekaweau, measured 60 centimetres (including the tail) and featured in Māori legend. It was last reported in the Urewera in 1870, and the only likely specimen is held at a French museum.

Over 90 species of skink and gecko remain, but about 40% survive only on rat-free offshore islands. Many species on the mainland are threatened by rats, cats, dogs and stoats.

Frogs

Three extinct frog species are known. There are four living species, two of them confined to small islands.

Fish

The grayling or upokororo was an important fish in streams and rivers, and a useful food during Māori and early European times. It went rapidly from abundant to rare between the mid-19th and early 20th centuries, and is now presumed extinct. This may be linked to the introduction of trout into rivers and lakes, but grayling also vanished from trout-free waters.

Plants

There is little evidence of New Zealand plant extinctions since human settlement. The slide towards extinction tends to be slower than for animals – plants may be damaged by browsing, but still continue to breed. Some dangers to plants, such as fire, are restricted to a local area, unlike predators which can travel widely and use scent to track their prey. Other processes affecting plants are gradual rather than sudden. But without intervention, more plants will be lost in the long term.

Four plants are known to have become extinct in recent times. The best-known is Adams mistletoe. It suffered a reduced habitat, loss of the birds that pollinated it and dispersed its seed, browsing by possums, and over-collecting by plant enthusiasts.

Another extinct New Zealand plant is Lepidum obtusatum, a species of coastal cress.

Many more plants are threatened.


Causes of extinctions in New Zealand

The human factor

The causes of extinctions in Australia and North America are still debated, but there is little doubt that humans are the cause of recent New Zealand extinctions. Research has implicated:

  • the mammalian predators introduced by humans
  • changes in habitat caused by humans and rats
  • habitat destruction by human-caused fires
  • direct predation by people.

No link to ice ages

The New Zealand extinctions differ from those in other places because of their lateness. Almost all species made it through the coldest part of the most recent (Ōtira) ice age, which is when the American extinctions took place.

Role of disease

Diseases are commonly suggested as a cause of extinction, but it is rare for any disease to wipe out its host species. The only foreign pathogen to be found in New Zealand birds is bird pox, which has had little impact on the species involved. Diseases usually affect closely related species, but in New Zealand, for example, some wrens and frogs died out, while related species survived nearby.

Bird loss: impact on ecology

The killing off of huge seabird populations by rats on the main islands had the most significant ecological effect on New Zealand. With their loss, the cycling of large quantities of nutrients from the sea to the land has stopped. Extinct land birds included species that pollinated and dispersed the seeds of forest trees and shrubs, and the large plant-eating birds whose browsing may have shaped growth patterns of some New Zealand vegetation.

Altered habitats

The habitats of the most endangered species are not those they enjoyed before humans arrived. Former ecosystems may have changed because of the extinction of invertebrates, such as some species of wētā, and vertebrates, such as the seabirds. Indeed, major nutrient sources may no longer be present.

Lessons from the past

Globally, the New Zealand extinction event is the most recent of all the late Quaternary-period extinctions. The rich record of species in fossil deposits makes this one of the best understood extinction events. While extinct species cannot be revived, it is a warning that the present generation act to ensure that no more species become extinct.


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How to cite this page: Richard Holdaway, 'Extinctions', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/extinctions/print (accessed 28 May 2017)

Story by Richard Holdaway, published 24 Sep 2007