The Beaks Of The Ancient Moa Determined Their Diet

Giant moa were hunted by the equally giant Haast's eagle. John Megahan/Wikimedia Commons
Josh Davis 15 Jan 2016, 20:08

The moa, which used to wander the wilds of New Zealand, were some of the largest birds to have ever existed. In isolation from the rest of the world for tens of millions of years, the birds lost their ability to fly and grew to huge proportions, filling the roles normally taken by mammals in the rest of the world. So far, nine species of the now extinct birds have been described from both the North and South islands, but how they all lived side by side, despite all seeming fairly similar in appearance, has been difficult to explain.

A new study has, however, suggested that while the birds may look the same, the beaks of the birds were sufficiently different to allow them all to occupy different feeding niches, or places in the ecosystem. This means that the birds would not have been in competition with each as they roamed the forests and grassy plains of New Zealand, as they relied on differing foods. The study is published in the Proceedings of the Royal Society

The researchers took the partial skulls from the nine species of moa and scanned them using medical CT machines to create 3D models for each species. Because there have been no fully complete moa skulls ever found, they digitally reconstructed the missing parts to create accurate models for each. They then turned to the mummified remains of a moa head in order to understand where the muscles would have attached to the neck and beak. From this, they were able to calculate the forces and stresses that would have been placed on the birds’ beaks as they fed.

They found that the different species of moa had beaks adapted to differences in their diet, not unlike what Darwin found with the Galapagos island finches. This goes against what previous studies have suggested; that it was the body size that determined the birds’ diets. One species of moa, A. didiformis, had a short, sharp-edged beak that would have been ideal for cutting vegetation, while another species called E. curtus had a broader, weaker bill that would have been more suitable for plucking soft plants and fallen fruit.

The moa were hunted to extinction within one hundred years of humans being on New Zealand. Joseph Smit/Wikimedia Commons

Interestingly, these findings about the feeding behavior of E. curtus actually back up previous suggestions that the bird acted as a fruit disperser, not unlike cassowaries in the rainforests of Australia and New Guinea do today. In addition to that, the information about what the birds ate also allows researchers to speculate about how they moved within their habitat, as animals that feed predominantly on fruit are forced to roam large distances to get enough food.

The birds used to inhabit both islands in New Zealand, with species being described from a range of habitats, from the uplands to the lowlands, forests to coasts. The biggest of the moa reached around 250 kilograms (550 pounds) and stood 3.6 meters (11.8 feet) tall, while the smallest was around the size of a sheep. Because they had been isolated for such a long time, when humans arrived on the islands around 1300 C.E. the moa were perhaps naive to the threat. Within just a hundred years, the newly arrived people had managed to wipe out all nine species of moa from both islands through hunting activities.   

Top image in text: The mummified head of  moa with reconstructed muscles painted on. Peter Johnston 

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