Fast Food

New evidence suggests the moa was wiped out within 50 years

By Allan Coukell

The last moa steps from the forest and stands, blinking, in the sunlight. He is reddish brown, with hints of purple, or perhaps blue-grey (from this distance it is hard to tell). Perhaps he is Anomalopteryx didiformis, the little bush moa, a metre tall and less than 40 kilograms. Or another of the smaller, forest dwelling species. Even from here, we can say with confidence that he isn't Dinornis giganteus - the last of those giants disappeared more than a generation ago.

And then the last moa hunter enters the clearing. He knows that these birds, once plentiful, are now rare. Perhaps some instinct of his lifetime in the bush tells him that this is the very last bird. (And if so, what of it? No point letting the thing die of old age!) Whatever his thoughts, our hero steps quickly to the uncomprehending beast, and dispatches it. Dinner. Extirpation.

Nobody knows, of course, exactly how the last moa met his end (the arbitrary male designation allows me to avoid any question of which came last, the moa or the egg). At present, the standard view of moa extinction is that the birds were eliminated by a combination of hunting and habitat loss over a long period, perhaps 600 years.

However, new evidence suggests that moa may have been hunted to extinction within a century of human arrival on these islands.

Writing in the journal Science, Richard Holdaway, a Christchurch palaeobiologist, and Chris Jacomb, of the Canterbury Museum, argue that the low reproductive rates of moa made them particularly vulnerable to human predation - a scenario they describe as a "blitzkrieg" extinction.

The authors start by assuming an initial moa population of 158 thousand - a cautious assumption, which is roughly double previous estimates. They estimate moa reproduction rates based on knowledge of other long-lived birds (such as cassowaries and eagles), combined with fossil evidence that moa typically laid only 1 or 2 eggs in a clutch.

Making these assumptions, it turns out that even low-level consumption of moa by a small, slowly growing human population (say, 100 individuals in the initial population consuming 10 female birds per week) would have been enough to wipe out the moa in 160 years. Assume a "most likely" scenario of more people to start with (200) plus faster population growth and additional moa deaths from habitat loss - almost a certainty - and you have complete extinction in as little as half a century.

But could a tiny human population really have found every last moa? Trevor Worthy, a Nelson palaeontologist, says "yes". Open eastern habitats were largely destroyed by burning, and western forests, "although frightening for some city dwellers", would only have had one moa every 15 kilometres or so. "You could find where they'd be because they'd have favourite food trees and they'd have to go to drink every day - things that anyone who deals with animal hunting would sort out in a couple of months."

Others are more skeptical. Atholl Anderson, an professor of prehistory at the Australian National University in Canberra and author of a book on moa, suggests that Holdaway and Jacomb have interpreted their results in a way that exaggerates the difference between the "standard" and the "blitzkrieg" scenarios.

Anderson also argues that, although the main moa population in open areas would have been rapidly hunted to extinction, more remote districts were probably visited much less often. "Areas of broken hill country with scrubby vegetation and deep gorges - inland Otago, for example - may have retained small moa populations for considerably longer." He also questions the assertion by Holdaway and Jacomb that no moa remains are found at Maori campsites younger than the fourteenth century.

Perhaps more important than the precise time over which the moa were hunted to extinction is the fact that such an occurrence is far from an isolated incident.

The evolutionary physiologist Jared Diamond, writing in the same issue of Science, says similar rapid extinctions of large animals probably occurred every time humans found new hunting grounds where the local wildlife had no natural fear.

Nor did the extinctions end with the disappearance of the big and the slow.

In tropical rain forests around the globe, at least 4000 species become extinct each year. The number of New Zealand species at risk of winking out is not known. Indeed, the number of New Zealand species is a mystery full-stop - of the estimated 80 000 species perhaps 40% have been described.

Dennis Gordon, a NIWA scientist who recently convened a conference on New Zealand's biodiversity, likens our lack of knowledge to a library of unread books: "we haven't even finished the first chapter, and the great tragedy is that we are losing the species around us before we can even turn the next page."

Jared Diamond puts it even more bluntly. "I wonder what the Maori who killed the last moa said - 'Your ecological models are untested, so conservation measures would be premature'? No, he probably just said, 'Jobs, not birds,' as he delivered the fatal blow."

© Copyright New Zealand Listener 2000 (29 April, p33) Reproduced by permission