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1 April 2003 The End of the Moa in Aotearoa
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New Zealand, or Aotearoa, the Maori “land of the long white cloud,” lies at the southern apex of the Polynesian Triangle in the South Pacific Ocean. In this book, those with an urge to explore “the land that time forgot” can learn what Aotearoa offered before and after our species arrived. The authors of The Lost World of the Moa detail the biogeography of 11 species of extinct moa, up to half a ton in weight, which skulked through forest and shrublands like cassowary rather than holding their heads up like an emu or ostrich. In the South Island, a top carnivore, the teratorn-size Haast’s eagle, preyed on moa. The roll call of Aortearoa’s avian extinctions also includes mysterious flightless adzebills, rails, and wrens.

Aotearoa originated over 56 million years ago, when a land that is now the size of the British Isles split off from Gondwana and, in glorious isolation, evolved diverse terrestrial feeding guilds out of its avifauna. The interior of prehistoric New Zealand had no mammals beyond three bats, two of them ground feeders. The terrestrial fauna included the iguana-size tuatara, small skinks and other small lizards, leiopelmid frogs, and giant flightless insects such as wetas.

In the absence of predatory or scavenging mammals, it is no surprise that natural deposits yield whole skeletons of moa and other birds, along with feathers, dried tissue, eggshells, gut contents, gizzard stones, and tracks. Pyramid Valley and its unusual marsh harbor numerous skeletons of moa and other birds. Judging from the size of fossil moa trachea, some species of moa must have outdone trumpeter swans and whooping cranes in their wild cries.

Worthy and Holdaway trace range changes of the moa and moa habitats back to 20,000 years ago, into the last ice age. Despite accompanying changes in climate, vegetation, and fauna (moa ranges included), the authors report no moa extinctions until very late in the Holocene. “Overchill” fails the test as a cause of moa extinction. Very soon after Polynesian colonization, however, only 700 years ago, moa (the collective noun used by the Maori) vanished. We then see the very last of the devastating prehistoric losses of large animals that began in Australia 50,0000 years ago, struck Japan 20,000 years later, and, just 3000 years ago, swept into the Polynesian triangle to the detriment of many species of birds, especially flightless ones. Worthy and Holdaway believe avian extinctions began in New Zealand 2000 years ago.

Worthy and Holdaway report the surprising extinction of many small animals, including flightless or ground-nesting small birds, before the loss of moa. They suspect that the first people to land in Aotearoa did not colonize. Instead, whether intentionally or not, they left behind a hallmark of things to come, the Pacific rat, Rattus elegans. Its bones have been radiocarbon-dated to a time significantly before the settlement of the Maori about 700 years ago. Moa survived until after the extinction of many small animals, doomed by the rats.

On a brief visit to New Zealand in the 1970s for a conference of the International Quaternary Association, I first learned of an unusual discovery. Paleoornithologist Ron Scarlett reported discovering the fossil bones of an extinct owlet-nightjar (Caprimulgidae) that was related to an Australian genus, Aegotheles. Although in the same family as nighthawks, whippoorwill, paraque, and other goatsuckers—agile feeders on flying insects—the Australian owlet-nightjars feed on the ground. More robust than its Australian relative, the New Zealand species would have been a poor flier at best and an obligate ground feeder, certainly not in the same niche as North American nighthawks.

In the 1970s paleontologists increasingly adopted the view, which originated with Sir Richard Owen over 100 years earlier, that the moa of New Zealand must have succumbed to human hunting. I imagined that unless some other forcing function could be defended, so did all the other extinct species in New Zealand. But how could an owlet-nightjar, a crepuscular or nocturnal ground feeder, suffer the same fate as the moa? Beyond that, why would moa hunters pay attention to, much less exterminate, even smaller species such as the acanthisittid wrens, flightless passerines?

Worthy and Holdaway report that the new species of owlet-nightjar very likely consumed wetas, New Zealand’s giant flightless crickets, along with other giant insects. Along with leiopelmid frogs and the tuatara, the giant flightless insects survive on small offshore islands. What eliminated all of these animals on the large North Island and on the larger South Island of New Zealand?

Worthy and Holdaway indict the Pacific rat as the exterminator of small terrestrial species. The rats wiped out the flightless wrens on the two main islands, as well as the giant insects, indirectly including the stocky caprimulgid in their toll by depleting its food supply. The Pacific rat is a poor swimmer, and as a result near-shore small islands offered a refuge for ground dwelling small species otherwise at risk from rat depredations.

Thus, at least indirectly, the Polynesians triggered all extinctions. Worthy and Holdaway report rat bones radiocarbon dated to roughly 2000 years ago, long before the first evidence of colonization by Polynesians themselves. Beyond New Zealand, in at least a few other Pacific islands, small animal extinctions apparently preceded archaeological evidence of Polynesian settlement.

Less than 300 years ago Europeans began to settle in New Zealand, accompanied by many more species of lethal mammals: Norway rats (1772), cats and house mice (1830), black rats (1855), Australian brush-tailed possum (1858), European hedgehog (1870), and European ferrets, weasels, and stoats (1879–1885). Currently, the New Zealand government is struggling valiantly to stop the hemorrhage of extinctions. Those islands not overrun by predatory small mammals offer a potential refuge.

Out of a total fauna of 245 species of prehistoric birds, the list of avian extinctions in the last 2000 years is 66. Extinction struck only three of the 57 species of pelagic marine birds in New Zealand’s vast primordial breeding colonies of petrels, storm petrels, shearwaters, and albatross. Nevertheless, with the arrival of the Pacific rat and other mammalian predators, these ground nesters suffered fearful depletion or local extirpation.

Summarizing two decades of full-time work on new fossil excavations, as well as existing collections, and offering an up-to-date account of the biogeography of extinction beginning in the late Pleistocene, Worthy and Holdaway present a richly documented and well-illustrated account of dynamic changes in the late Holocene. The authors are more than entitled to their occasional opinions; for example, “The lack of understanding by many continent-oriented and, it must be added, Northern Hemisphere–trained biologists of both the importance of naïveté and the effects of rat and human predation in island faunas has held back the understanding of the cause of extinction on oceanic islands.”

PAUL S. MARTIN "The End of the Moa in Aotearoa," BioScience 53(4), 434-435, (1 April 2003).[0434:TEOTMI]2.0.CO;2
Published: 1 April 2003

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