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Scientists are probing fossilised moa dung in a bid to pin down exactly what the giant bird ate and what effect their grazing had on plant life.

Some moa were the world's biggest birds, weighing up to 240kg, and are thought to have heavily influenced the ecosystems in which they grazed.

Though the last of the birds only died out about 600 years ago, little is known about what they ate.

Landcare Research scientists Jamie Wood and Janet Wilmshurst and New Zealand scientists Alan Cooper and Trevor Worthy at the University of Adelaide aim to flesh out that knowledge using $768,000 of taxpayer funding over three years.

The national science academy today allocated the government money in Marsden Fund grants.

Dr Wood will examine 1500 specimens of fossil dung from rock shelters across southern New Zealand, using DNA tests on not only the large deposits attributed to moa but many smaller ones from unknown species.

The preserved dung will also be examined for seeds and leaf fragments to see what plants the birds ate in a effort to say what plants different birds, and even different genders in the same species, ate at various times of the year.

So far only five fossilised dung specimens have been analysed.

Some scientists have theorised that New Zealand's high proportion of small-leafed shrubs evolved to evade browsing moa.

Mr Worthy, a palaeontologist known as "Mr Moa' when he was based at Masterton, is an expert who used bone analysis to help slash the number of recognised moa species from 38 to one.

He will work with Professor Cooper, who used ancient DNA to show that there were actually only two families of moa, one on the North Island and one on the South Island and that variations in the bones were actually size differences between females and males.

The team will also study soil from virgin native forests to see how the composition of the forest understorey altered with changes to grazing by moa or introduced herbivores.