Blame Humans: New Research Proves People Killed Off New Zealand's Giant Birds
Moas were a diverse group of flightless birds that ruled over New Zealand up to the arrival of humans, the biggest of these mega-birds stood around 3.5 meters (12 feet) with outstretched neck. While the whole moa family—comprised of nine species—vanished shortly after the arrival of people on New Zealand in the 13th Century, scientists have long debated why the big birds went extinct. Some theories contend that the birds were already in decline due to environmental changes or volcanic activity before humans first stepped on New Zealand's beaches. But a study released today in the Proceedings of the National Academy of Sciences (PNAS) finds no evidence of said decline, instead pointing the finger squarely at us.
To find the moa's smoking gun, scientists analyzed two different sets of DNA from 281 specimens made up of four species: the South Island giant moa (Dinornis robustus), the biggest of the family; the heavy-footed moa (Pachyornis elephantopus); the eastern moa (Emeus crassus); and the coastal moa (Euryapteryx curtus). Instead of showing a slow, genetic decline, the DNA told a different story: moas were thriving even as humans arrived.
"The millenia preceding the extinction were characterized by a remarkable degree of genetic stability in all species," the researcher, headed by Morten Allentoft with the University of Copenhagen, write in the paper.
In fact, the Allentoft and his team found that some populations were even on the rise right up to the end. And the end came fast, so fast, in fact, that it left no imprint in the four species' genetics as it usually does when species genetically constrict. Just a century or two after the arrival of humans on New Zealand, all nine moa species were gone for good. The scientists call this "the most rapid, human-facilitated megafauna extinction documented to date."
These results tell a very different story than a 2004 DNA study that implied the giant birds may have already been on life support before humans provided the death blow. But this research was "based on limited mitochondrial DNA (mtDNA) data," according to the new study. Here, Allentoft and his team combined mtDNA with another type of genetics analysis—nuclear microsatellite genotyping—giving them a broader view of population trends.
This squared with archaeological findings as well, which show mounds of butchered birds and eggs. Like many island animals that have known humans, the moas were likely unafraid, making them easy to approach and kill.
"You see heaps and heaps of the birds' bones in archaeological sites," Allentoft told Science News. "If you hunt animals at all their life stages, they will never have a chance."
The moa's demise took another species with them, their only predator: Haast's eagle (Harpagornis moorei). A massive predator, the Haast's eagle was likely among the heaviest raptors in the world, even if its wingspan was similar to many other large eagles. Scientists theorize that Haast's eagle quickly vanished once humans had hunted its prey to oblivion.
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