New Zealand's flight path to disaster

By JACK GRANT-MACKIE*

Trevor H. Worthy and Richard N. Holdaway: The Lost World of the Moa

Canterbury University Press $169.50

Few people are aware that, as the authors claim, New Zealand has a better record of the birds that lived over the past 100,000 years than any other area of the world. Our avifauna is diverse, unique, special, intriguing - and, to a large extent, extinct.

When we think of New Zealand's fossil birds most of us know of little beyond the moa, and perhaps our giant eagle. Worthy and Holdaway document a much larger fauna that has disappeared since the arrival of humans. They describe the extinction of 66 bird species and another five extinct in our area but surviving elsewhere. This is nearly one-third of all birds formerly breeding in New Zealand. And their loss has occurred in the past 800 years or so.

This book of more than 700 pages is a comprehensive, in-depth, scholarly work which fully examines the makeup of our lost avifauna, the way its members interacted, their distribution, preferred habitats, morphology, origin and evolution, and the timing and causes of their extinction. It pulls together the results of 150 years of research, much of it published over the past 20 years by the authors. No account of this magnitude, depth and coverage has been previously attempted for our birds. It is, in addition, an eminently readable, deeply interesting, and well-illustrated account which will find a valuable place in the libraries of high schools, biological and earth science teaching and research establishments, and ornithological societies, as well as being suitable for, and usable by, the amateur bird-lover.

There is a worldwide interest in New Zealand birds because of their unique features and because of our successful conservation efforts. Moa were the largest birds to have lived on Earth and the only birds to have completely lost their wings; our eagle was the biggest; kiwi the only one with nostrils at the tip of the beak and with a bigger egg-to-body ratio than any other; kakapo the heaviest and only flightless parrot; huia had more obvious differences between the sexes (in the beak) than any other bird; our extinct wrens were the smallest flightless birds and the only flightless songbirds. This book will also feed the international market, and, in its American edition, has already been favourably reviewed in both Science and Nature.

The first 200 pages deal with the moa. There is a fascinating account of the early European finds: the staggering abundance of the large bones, including that wagon-loads were send off for crushing as fertiliser; Sir Richard Owen's first prediction of the presence in New Zealand of a giant flightless bird, based upon a single incomplete thigh bone sent to him in England in 1839; the bewildering variety of shape and size of the bones that led to moa being classified into more than 50 species in some two dozen genera (now reduced to 11 species in six genera); and the finds of moa footprints, feathers, skin, mummified flesh, and eggs.

Their fossilised crops and gizzards, found in swamps as at Pyramid Valley in Canterbury, have preserved the plants they ate, showing us that they mainly cropped shrubs and small trees but also grazed on the ground.

There is a detailed description of moa anatomy, the variations among the species, and what those variations indicate regarding the way the different species lived. Distribution patterns are outlined, with some species confined to one main island or the other (only one is found on Stewart Island, and moa never reached the Chathams), some restricted to coastal environments, others to inland forests, and one to South Island high country.

Traditionally we have assumed that moa and kiwi had a common origin in a flightless bird that was in our region when the ancient Gondwanaland continent broke up and New Zealand drifted away from the Australian-Antarctic segment some 80 million years ago. Evolution of both from that ancestor was thought to have occurred entirely within New Zealand. Modern DNA studies suggest that moa indeed probably had that origin, but kiwi developed later from the same stock as emu and cassowary. That means kiwi must have come to New Zealand after the breakup of Gondwanaland - so how did it reach here? Worthy and Holdaway examine this conundrum, too.

All the other birds of the New Zealand fauna, living and extinct, are treated, including some, like the so-called Queensland moa and Chatham Island sea eagle, that are regarded as recording errors (the Queensland moa, recorded in 1884 as a new species, was a New Zealand bone taken to Australia, and the sea eagle record was based on bones of the North American bald eagle mixed in with Chatham collections). There are extensive discussions of the more significant species - for instance, nearly 100 pages on the extinct giant Haast's eagle - concerning their origins and evolution, feeding preferences, reproduction and nesting.

Extinction is the prime cause in writing this book. Significant effort is expended considering its causes and process. For a long time we have sought to minimise the effect of human intervention as a cause of extinction in the New Zealand milieu. Early Polynesian settlers were cast as careful conservators of their food resources. Worthy and Holdaway examine this claim in the light of the bone contents of their middens and a huge number of reliable radiocarbon and other dates. They demonstrate three waves of extinction resulting from arrival of the Pacific rat about 2000 years ago, of Polynesian settlers some 800 years ago, and of European predators a couple of hundred years ago.

Their conclusion that humans have been responsible is inescapable. The first Pacific rats, which came with Pacific voyagers who did not settle here at that time, devastated the small birds (and no doubt large invertebrates such as weta). Early Maori found plentiful numbers of large flightless birds (geese, ducks, adzebills, as well as moa) which until then had no ground-dwelling predators and so were not frightened of humans. Moa were extinct within about 200 years of their arrival.

Interestingly, kuri, the dog brought by Maori, is not counted as having had any ill effect on the birds. They were kept tethered and did not escape to form feral packs as did those brought by Europeans.

The third wave of extinction came with the combination of extensive habitat destruction by Europeans and the introduction of further predators. Of the 12 species of predatory mammals introduced by humans into New Zealand, 10 came from Europe, and their influence, and threat, continue to this day.

Worthy and Holdaway have a wealth of knowledge of our young fossil birds, and no one else working here could have written such a book. They point to various issues still to be resolved, new forms still to be described, relations still to be explained. All this will be done in due course, but regardless of this their book will remain a most important reference for many years.

* Jack Grant-Mackie is a retired palaeontologist and a research associate in the department of geology, University of Auckland.