Nine species of giant, flightless birds, known as moas, suddenly went extinct within two centuries of humans’ first arrival to New Zealand. Coincidence? No, a team of geneticists, biologists and archeologists recently wrote. The scientists found evidence that moas thrived before Polynesians colonized the islands in the 13th century.

The scientists analyzed genetic remains from 281 individual birds from four species of moa. The researchers looked for signs of dwindling moa populations in the 4,000 years before humans arrived. When animal populations shrink dramatically, their genetic diversity also decreases. Instead, the moa had a healthy variety of DNA, which suggested strong populations.

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For example, the 3.6 meter (12 ft.) tall South Island giant moa (Dinornis robustus) had an estimated population of 9,200 individuals that may have been growing. Although another species, the 1.5 to 1.8 meter (4.9–5.9 ft.) tall eastern moa (Euryapteryx crassus), showed signs of a major historical die-off, that reduction in numbers likely occurred more than 17,900 years ago, thousands of years before humans arrived. Euryapteryx crassus had recovered and seemed to be thriving in the eastern lowland forests of New Zealand by the time humans arrived.

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“These findings point strongly toward human contact as the only factor responsible for the extinction,” wrote the scientists in Proceedings of the National Academy of Sciences.

“Elsewhere the situation may be more complex, but in the case of New Zealand the evidence provided by ancient DNA is now clear: The megafaunal extinctions were the result of human factors,” said lead author Mike Bunce of Curtin University in Australia in a press release. “We need to be more aware of the impacts we are having on the environment today and what we, as a species, are responsible for in the past.”

Illustration: “Polynesians Hunting Giant Moa,” by Heinrich Harder. Credit: Wikimedia Commons