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Data courtesy of "Rapid Extinction of the Moas" article.

Courtesy Errol Fuller's Extinct Birds.

POSTED 23 MAR 2000 You probably don't give the moa much thought, this ungainly and utterly extinct flightless bird from New Zealand. Like the equally extinct dodo, the moa apparently carried signs saying "Free meal enclosed" when the first humans began settling sometime around 1280 AD.

Before long, the bird was history -- "survived" only by bones littering archeological sites throughout New Zealand. It's the same story that, some archeologists believe, has occurred worldwide -- people settle a new area, and the big animals wind up on dinner plates.

According to some scientists, many cool animals in the Western Hemisphere -- including the saber-toothed cat and relatives of the camel -- were hunted to extinction shortly after humans arrived via the Bering land bridge 10,000 or so years ago. Richard Holdaway, a paleobiologist from Palaecol Research in Christchurch, New Zealand, has given the moa a lot of thought, and even burned up computer time trying to figure out how quickly the big bird bit the dust. The conventional wisdom said that the 11 species of moas were exterminated over the first 600 years after settlement, but Holdaway argues that's way too long.

For one thing, it's now thought that people arrived in New Zealand around 1280, rather than 1000 AD. That by itself would cut the deathwatch duration in half. But a computer model and archeological evidence indicate that the time must be halved once or twice more.

Howzee knowit?
The computer model analyzes changes in a population using features like birth rate, survival rate and immigration, Holdaway wrote in an e-mail interview. "The strength of the method is that it assigns values for these variables to each age class in the population and then assesses the changes that occur in all these age classes through time."

Clearly the first Polynesians, now known as Maoris, had a taste for moa -- their early habitation sites are littered with moa bones. Judging by surviving large birds in New Zealand, Holdaway says moas probably reproduced slowly, and between hunting and habitat loss, people could have extinguished them in 50 to 160 years.

In cranking up the computer model, Holdaway and colleague Chris Jacomb used conservative assumptions to avoid underestimating the time to extinction. They doubled the estimated moa population, for example, and ignored the effects of eating moa eggs and birds younger than one year.

Still, no matter how they diced the data, the moas split the scene rather quickly:

If 100 Polynesians arrived, and their population grew 1 percent per year, and 20 people ate one female moa per week, and we ignore any decline due to habitat altered by people, the birds would have gone extinct in 160 years.

If 200 people arrived, the population grew 2.2 percent per year, 10 people ate one female moa each week, and habitat loss is factored in, the birds would have vanished in just 50 years.

To test whether the model was cranking out plausible numbers or pure garbage, Jacomb looked at a well-preserved archeological site called Monck's cave. Although moas were definitely eaten by residents of an earlier cave close by, no moa bones remained at Monck's, which was occupied around 1400 AD.

Eerie implications
Previously, that might have been considered evidence that moas had survived 350 years after colonization, on the assumption that the Polynesians reached New Zealand around 1000 AD. But the newer date for arrival, between 1250 and 1300 AD, reinforced the model's conclusions, writes Holdaway. "The model predicted that moa would have ceased to be a component in the diet in the area about 1400 AD; the Monck's Cave deposits contain only fish, shellfish, and a few small birds"

Just as hungry people these days can't resist fatty, greasy, high-protein fast food, he writes that "It is unreasonable to suggest that people would have deliberately ignored a large and familiar source of protein and lipid if it had been available."

Holdaway's calculations help reinforce the "overkill hypothesis." The idea that people can hunt animals to extinction was first proposed decades ago by Paul Martin, an ecologist at the University of Arizona. A beast as terrifying and edible as the mammoth may have been exterminated from North America in as little as a century, says Stanley Temple, a professor of conservation biology at University of Wisconsin-Madison.

In terms of present-day conservation, when extinction rates are soaring, the research has an unsettling message, Holdaway concludes. "A few people with a limited technology can make a large impact. And the results of that action (predation and habitat loss) is NOT obvious to the people engaged in the practices."

Temple, however, notes that humans have by now hunted essentially the entire world, so every element of the moa situation cannot be repeated. Nevertheless, he stresses that birds like the guans, in the New World tropics, are being hunted heavily because they're such good food -- equivalent to the pheasant or quail.

More broadly, Temple cautions that the study is another indication that, "human over-exploitation regardless of circumstances or species does have the potential to cause the extinction of populations very rapidly."

-- David Tenenbaum

Hunting and the Likelihood of Extinction of Amazonian Mammals, Richard Bodmer et al, Conservation-Biology, 1997; 11 (2) 460-466.