Dead as a dodo: the extinction connection

By John Pickrell 22 July 2013
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Great waves of extinction have followed human migrants since they first set off across the planet, says John Pickrell.

AS ANCIENT PEOPLES explored and colonised the Earth they encountered strange and wonderful creatures along the way. But wherever our ancestors trod, many of these animals disappeared soon after in great waves of extinction. Climate change played a role, but evidence against human hunters seems damning.

Beginning about 50,000 years ago in Australia, many large animals disappeared, including massive, lumbering herds of wombat-like diprotodon, marsupial lions, and gigantic species of kangaroo, monitor lizard and horned tortoise. Here, Aboriginal burning practices are implicated, as well as hunting.

In North America, about 13,000 years ago and soon after the first Clovis people arrived from Asia, elephant-like mastodons disappeared. Other animals long gone from the Americas include mammoths, sabre-tooth cats, horses (later reintroduced by Europeans), camels and giant species of bear, sloth and armadillo.

The dodo of Mauritius has long been the totemic symbol of something destined for the evolutionary waste basket, but now it seems that it was one among many, many flightless island birds that disappeared worldwide, huge numbers of them in the Pacific.

Vanishing Pacific birdlife

The remote islands of the eastern Pacific were the last habitable regions on the planet to be colonised by people. Human migrants arrived in Australia and the Americas tens of thousands of years ago, and 3500 years ago Polynesians had made it as far east as Samoa, Tonga, Fiji and Vanuatu.

The more remote Pacific Islands of Hawaii, New Zealand and Rapa Nui (Easter Island) still lay ahead of them, and were perhaps more difficult to reach, until technological innovations made the journeys easier 700–900 years ago.

New research from the University of Canberra now indicates that this sudden burst of migration was likely followed by what may have been the most concentrated wave of human-induced extinctions our planet has ever endured. Researchers led by ecologist Professor Richard Duncan have calculated that about 1000 bird species became extinct after Polynesian colonists arrived on the 269 largest Pacific Islands, representing about 10 per cent of modern global bird diversity (9993 species).

As the fossil record from these islands is poor, the researchers instead looked at how many living birds are either missing from, or are represented in, the fossil record today, and then used that to estimate numbers of extinct birds that might be missing from the record.

They only looked at non-passerine birds (a mixed bag of species including everything but the songbirds) and found that somewhere between 983 and 1300 of them died out. We know that some songbirds suffered extinction too, so the total figure is likely to be even higher.

For a number of reasons, island birds were doomed. They had few native predators – and therefore no innate fear of people – and if they were flightless they were easy to catch, and often plump and tasty. This made them ready sources of protein for hungry Polynesian mariners.

Birds on small islands doomed

Other factors made some species more susceptible than others. When people arrived on islands they felled large areas of lowland forest for farming, timber and fuel, so birds that called these habitats home stood little chance (the lonely statues of Easter Island are all that remain after people there felled their forests into oblivion).

Flightless birds on larger and more mountainous islands were more likely to survive. This is why species such as the kiwi, takahe and kakapo of New Zealand persisted when Europeans arrived, but flightless birds on neighbouring islands, including many Pacific rails, did not.

How lucky we are that species such as the kakapo cling on today, but what a thrill it would be to encounter moas, marsupial lions and mastodons in the wild. It seems that waves of extinction have been a fact of life in the history of human expansion across the Earth, but that doesn’t make it any less sad to read through the long rollcall of species that have been lost.

John Pickrell is the editor of Australian Geographic. Follow him on Twitter @john_pickrell.