Ancient DNA analysis has revealed the safe havens where New Zealand seabirds found sanctuary from early human hunting.
The arrival of the country's first settlers more than 700 years ago had a profound impact on many species of New Zealand wildlife which had never before been hunted by people.
In a newly published study, an international research team led by Otago University has used DNA analysis, along with computational modelling and radiocarbon dating, to reconstruct population histories for prehistoric seabirds around coastal New Zealand.
Dr Nic Rawlence, who carried out the genetic study, said the team found a distinctive pattern, where shag populations from the Stewart Island region were little affected by human hunting, while mainland populations were rapidly decimated.
"There was a loss of more than 99 per cent of their population size within 100 years of human arrival," he said.
"These once heavily-hunted mainland populations now occupy only a fraction of their prehistoric range, having never really recovered."
The study suggests that the mainland populations survived on just a few rocky islands off the South Island's east coast.
"By comparison, the Stewart Island populations have experienced a relatively stable history," Dr Rawlence said.
Associate Professor Ian Smith, an Otago University archaeologist involved in the study, said it seemed these contrasting wildlife histories reflected differences in prehistoric human-hunting pressure.
"Interestingly, recent archaeological studies suggest that human numbers declined in the Stewart Island region around 1500 AD, a factor which seems to explain why wildlife persisted in this region."
Project leader Professor Jon Waters said scientists had long argued about the causes of prehistoric wildlife declines and extinctions -- some pointing the finger at humans, and others attributing the shifts to climate change.
"By showing drastically different wildlife histories--between regions that are climatically similar--we can start to understand the major impact of prehistoric human hunting, which differed across space and time."
The study, published in the leading journal Molecular Ecology, was funded by the Allan Wilson Centre and the Marsden Fund, and included team members from the Universities of Otago, California, and Arizona, as well as Canterbury Museum and the Museum of New Zealand Te Papa Tongarewa.