Moa beaks determined their diets - study

The extinct giant Haast eagle attacking little bush moa (John Megahan / supplied)
The extinct giant Haast eagle attacking little bush moa (John Megahan / supplied)

New Zealand's nine species of moa could co-exist happily because, surprisingly, they had very different diets, Kiwi and Australian researchers say.

Using medical scanners and the same software used to assess building strength after the Canterbury earthquakes, researchers created 3D models of each species' skull to learn more about the way the giant flightless birds ate.

Conventional thought on the moa, which roamed New Zealand until the 15th century and were some of the largest birds to have ever existed, was that the big difference in size between species determined how they foraged.

The largest species - the South Island giant moa - weighed up to 240kg, while the smallest – the upland moa – was the size of a sheep. 

But it turns out the different strength and structure of the herbivores' beaks influenced their diet.

The reconstructions of the skulls, held at Canterbury Museum and Te Papa in Wellington, were painstakingly made using scans of mummified remains.

"This wasn't a simple job as we didn’t have a single skull that was perfect so we used sophisticated digital cloning techniques to digitally reconstruct accurate osteological models for each species," study author Professor Paul Schofield from Canterbury Museum says.

The engineering software was used to test the strength and structure of the birds' skulls and then compared to the moa's living relatives the emu and cassowary.

Models of the skulls were used to test out different biting and feeding behaviours including clipping twigs and pulling, twisting or bowing head motions to remove foliage.

Second author Dr Marie Attard from the University of New England says the skull mechanics were "surprisingly diverse".

"The little bush moa had a relatively short, sharp-edged bill and was superior among moa at cutting twigs and branches, supporting the proposition that they primarily fed on fibrous material from trees and shrubs.

"At the opposite extreme, the coastal moa had a relatively weak skull compared to all other species which may have forced them to travel further than other moas in search of suitable food, such as soft fruit and leaves."

Dr Trevor Worthy, who also worked on the study, says new technology is giving life to old bones and getting scientists closer to understanding where the birds came from.

The study was published in the journal Proceedings of the Royal Society B today.

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