Ancient moas may have furthered the spread of beech forests by eating mushrooms.

Jamie Wood

Fossil poop reveals critical role of giant birds in New Zealand’s ecosystem

When the first humans landed on what is now known as New Zealand 700 years ago, they didn’t find mammals. Instead, they discovered giant birds called moas, as well as a host of other indigenous bird species. Soon, they had eaten many of them into extinction.

Now, by deciphering ancient DNA found in fossilized bird droppings, researchers have a better idea of the toll those extinctions took on New Zealand’s forests and shrublands. The study shows that mushrooms and other fungi were important to the extinct birds’ diets, and suggests moas had a strong hand in shaping New Zealand’s native landscape by helping fungi spread, says co-author Alan Cooper, an ancient DNA specialist at The University of Adelaide in Australia. Now that the moas are gone, “The forest has potentially lost a potentially major way to spread.”

“This paper is a clear example of the great potential of ancient DNA-based techniques,” says Melania Cristescu, an ecological geneticist at McGill University in Montreal, Canada, who was not involved in the work. Cristescu says she was surprised by how much information the DNA contained. “The authors were able to identify a wide variety of species and to reconstruct the ecology of an extinct species.”

Over the past decade, Jamie Wood, a paleoecologist at Landcare Research in Lincoln, New Zealand, has found hundreds of fossilized bird droppings, or coprolites, well preserved in caves and shallow sediments across the country. Earlier, Cooper and others had done some rudimentary DNA studies that showed that many coprolites came from five extinct species of moas and the kakapo (Strigops habroptilus), a critically endangered parrot. But the data provided few details about what these birds ate.

Since then, other studies have shown that more extensive, high-throughput sequencing of DNA found in poop has the potential to reveal much more information. Researchers used it for an in-depth study of the gut bacteria of ancient Americans, for instance, and to catalog the diets of mammoths. So Cooper, Wood, and graduate student Alexander Boast of The University of Auckland in New Zealand decided to study in greater detail the DNA from 23 coprolites collected from eight beech forests and shrublands across New Zealand’s South Island. The droppings ranged in age from 124 to 1557 years old. For comparison, they also sequenced poop DNA from living kiwis, ostriches, and several mammals.

They found a staggering variety of DNA from plants, mosses, fungi, and parasites, whose distribution indicated that each species had its own diet and its own set of parasites, the researchers report today in the Proceedings of the National Academy of Sciences. There was more variety in the poop from what were once beech forests than scrubland coprolites.

Two species, the upland moa and the South Island moa, had mosses and ferns in their diets, the researchers report, whereas the others did not. The upland moa also carried a parasite that it could have only obtained by eating pond snails or aquatic plants, suggesting this relatively small species focused on foods larger moas ignored. It probably searched for food in alpine areas, where aquatic life thrived in high elevation lakes, even though that’s not where coprolites are found.

Surprisingly, fungal DNA was among the most common type of DNA, particularly in poop from species living in beech forests. Among the fungus species that researchers found were bracket fungi, puffballs, and true mushrooms, many of which are brightly colored to look like flowers and attract animals that help spread fungal spores in their droppings. Until these findings, “The role of fungi in the diet of New Zealand’s extinct birds has been largely speculative,” says Landcare Research paleoecologist Janet Wilmshurst, who was not involved with the work.

The fungi found in coprolites are essential to the survival of beeches, and Cooper thinks moas played an important role in helping beech trees expand across New Zealand. Beech forests are well established in the country, but natural disasters have wiped out the trees in some patches, and they haven’t returned; that might be because they lacked the moas’ help, Cooper says. “Reconstructing even some of the major interactions can provide guidance” about how the flora, fauna, and landscape are connected—and how they may preserved, he points out. Foresters may want to find new ways to spread these fungi as well as plant new seedlings in places where the beeches have disappeared, for instance.

The new study coincides with the release of a preprint describing the genome of the little bush moa (Anomalopteryx didiformis), based on little bits of DNA found in a toe bone of a museum specimen. The team, led by Harvard University molecular ecologist Alison Cloutier, discovered that the genetics underlying the moas’ winglessness are different than those for other birds that don’t fly, such as the Galápagos cormorant. This first moa genome will help decipher other moa species’ DNA as well, Wood says. “Ultimately, the combination of genomics and palaeoecology will provide an incredibly detailed view of the lives of moa.”