Rats gnaw Maori arrival theory

DATE DEBATE: Research based on evidence from the kiore, or Maori rat, released today argues the first human's arrived in New Zealand around the late 13th century, not more than 2000 years ago as previously believed.

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Human colonisation of New Zealand began around the late 13th Century, and not more than 2000 years ago as previously argued, according to research published today.

The research looked at new radiocarbon dating of the bones of the Pacific rat, or kiore, and rat-gnawed native seeds.

An international team of researchers, led by Dr Janet Wilmshurst from Landcare Research, spent four years on the project.

Their work, published in the journal Proceedings of the National Academy of Sciences in the United States, concludes that the earliest evidence for human colonisation was about AD 1280 to 1300.

Their results do not support the findings from previous radiocarbon dating of rat bones, which implied a much earlier human contact of about 200 BC.

The original dates have been a source of debate since they were published in Nature magazine in 1996.

Critics say there is no supporting ecological or archaeological evidence for the presence of kiore or humans until the late 1200s, and they question the reliability of the bone-dating.

Dr Wilmshurst and her team re-excavated and re-dated bones from nearly all of the previously investigated sites.

They said all of their new radiocarbon dates on kiore bones were no older than 1280.

This was consistent with other evidence from the oldest dated archaeological sites, Maori whakapapa (genealogies or stories), widespread forest clearance by fire and a decline in the population of marine and land-based fauna.

"As the Pacific rat or kiore cannot swim very far, it can only have arrived in New Zealand with people on board their canoes, either as cargo or stowaways," Dr Wilmshurst said.

"Therefore, the earliest evidence of the Pacific rat in New Zealand must indicate the arrival of people."

She said the new date had important implications.

Firstly, because rat predation began only after 1280 and not earlier, rat-sensitive species could be diminishing faster than previously assumed.

Secondly, colonisation did not involve a protracted delay between initial discovery and subsequent colonisation, an idea implicit in earlier theories.

Instead, the first people arriving in New Zealand from tropical east Polynesia initiated an immediate and rapid transformation.

Dr Wilmshurst said the new dating of the rat bones was also supported by the dating of over 100 woody seeds.

Many of the seeds had tell-tale rat bite marks and were preserved in peat and swamp sites from the North and South Islands.

Dr Tom Higham, deputy director of the Oxford Radiocarbon Accelerator Unit at Oxford University, said the teeth marks could not be mistaken for that of another animal.

He said the rat-gnawed seeds provided strong additional evidence for the arrival of rats, and therefore humans, and were an indirect way of testing the veracity of the dates done on the rat bones.

Among the seeds analysed were some that were intact or bird-cracked, and the rat-gnawed ones occurred in both islands only after about 1280.

The researchers are now turning their attention to other islands in east Polynesia where similar controversies exist over the timing of initial human settlement.

- NZPA