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Big bird's slow breeding was its downfall


The mighty moa (Image: Zoological Society of London)

The biggest bird that ever lived, the mighty moa of New Zealand, was hunted to extinction partly because it took so long to reach breeding age, say scientists.

Dr Samuel Turvey of the Zoological Society of London and team report their findings in today's issue of the journal Nature.

The moa once walked New Zealand before being wiped out several hundred years ago by the Maori, the Polynesians who according to legend migrated to Aotearoa ("the land of the long white cloud") by canoe from the Cook Islands around seven centuries ago or longer.

The flightless, wingless bird, a cousin of the kiwi, stood up to 3.5 metres high and, at 250 kilos, was a plentiful source of meat.

But how could a small Maori population, armed only with close-range wooden weapons and traps, wipe out such a plentiful species in such a large country?

The answer, according to the new research, may be found in growth rings in the bones of these extinct giants.

These marks are common in many animal species and are caused by differing growth rates in changing seasons. But bird species do not have these rings as in most cases their growth phase is confined to less than a year.

The moa, though, was the exception.

Examination of rings in stored bones suggest that the two moa species, luxuriating in the safety of New Zealand's unique eco-system, may have taken several years to reach reproductive maturity and up to a decade to attain skeletal maturity.

That made them "extremely vulnerable" to hunting. If too many adult moa were caught too quickly there would have been no chance of replenishment, and the species, dominated by unreproductive birds, would have been placed under severe pressure.

A study published last November postulates that there was a crash in the moa population that occurred before the arrival of the first settlers.

Moa numbers may have been between three million and 12 million birds a thousand years ago but tumbled to just 159,000 before the Polynesians arrived, possibly because of avian diseases brought by migrating birds or of the local effects of volcanic eruptions.

As the moas had no natural predators, their numbers would have rebounded eventually, had it not been for the fateful intervention of humans, according to this theory.

Tags: indigenous-aboriginal-and-torres-strait-islander, climate-change, ecology, palaeontology