by Whit Gibbons

November 10, 2013

Once upon a time there lived a bird that grew taller than any NBA center. It did not live happily ever after, and the story of its demise provides a disquieting revelation of how quickly humans can drive species to extinction. Studies of the enormous flightless birds known as moas have confirmed that a small number of people can eliminate a large number of animals in a short time. The remarkable rate of extinction of the moas is a cautionary tale for us all.

Moas were the biggest birds ever to have lived on earth, some being more than 10 feet tall. They would have towered over today's ostriches. They were impressive ground-dwelling birds on the islands we now call New Zealand. As would be expected, moa eggs were gigantic. I once held one that had been obtained by the explorer Richard Archbold. A bird egg the size of an oversized football is dramatic. But the most remarkable feature of the one I held was that it had been laid more than 6 centuries earlier and was just a dead egg, not a fossilized one.

In the late 1200s Polynesian settlers, the Maoris, arrived on New Zealand. Maoris and moas did not mix well. By the time Columbus arrived in America, giant moas had been extinct for a century. The reason: Maoris could easily capture and kill the big birds. Having never encountered such a relentless land predator, moas had never evolved the ability to fly.

Human colonization rates and the level of exploitation of moas have been determined by radiocarbon dating and the examination of Maori hunting sites with moa remains. From this information, an estimate of 100 Maori settlers was used to approximate the increase in human population size and rate of habitat loss on the islands. Subsequently, mathematical models have simulated the sequence of events for the decades following the arrival of the Maoris.

The model was based on an estimated 158,000 moas living in New Zealand at the time of human settlement. The predicted rates of decline of moas were then determined in a variety of scenarios, with the most conservative figures being used for each variable in order not to underestimate the time necessary for moa extinction to occur.

The maximum time for extinction of all of the giant moas in New Zealand would have been slightly over 150 years even without a loss of moa habitat and with an assumption that Maoris did not eat moa eggs. However, habitat loss did occur, and when an omelet big enough to feed a family was in the offing, eggs undoubtedly were taken. Using the more realistic figures that include habitat loss, the model indicates that moas became extinct less than a century after the first Maori canoe came ashore.

The significance is not that we can pin the loss of a fabulous group of birds on the Maoris. Virtually all colonists in all parts of the world can be held responsible for the elimination or severe decline of species that had not before encountered humans as predators. The important feature is that an original human population of only 100 people could eliminate moas so quickly.

The lesson for us in modern times is that small numbers of humans can still eliminate species simply by removing them from their native habitats. Exploitation for commercial profit for the restaurant trade, the pet trade, or for bogus medicinal cures (e.g., rhinoceros horn) can quickly bring a species to extinction. Many of today's birds and reptiles as well as large mammals that take several years to reach maturity and have low numbers of offspring are unable to sustain high adult mortality rates. They can readily become victims of human exploitation.

The message sent by the extinct moas is an important one: A tiny proportion of the world's human population could eliminate one or more of our remaining large species in the near future. We must be vigilant to prevent such an outcome.

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