New Zealand's now extinct giant moa survived for 40,000 years of significant climate and environmental changes without suffering large population slumps, new research shows.
An international team of scientists involving researchers from University of Waikato and Landcare Research has used ancient DNA from moa bones to conclude population numbers remained stable until the arrival of humans in New Zealand around 1280 AD.
The researchers say the study provides "overwhelming evidence" that the extinction of moa occurred due to overhunting and habitat destruction, at a time of relative climatic stability.
The giant birds - measuring up to 2.5m high and weighing 250kg - were the largest herbivores in New Zealand's pre-human environment but were quickly exterminated after the arrival of Polynesian settlers.
Now, the new study, undertaken by researchers from the University of Adelaide's Australian Centre for Ancient DNA, the University of Colorado, and the University of Waikato and Landcare Research, has revealed how the bird managed to adapt and overcome major environmental changes.
"Until now it has been difficult to determine how megafauna responded to environmental change over the past 50,000 years, because human arrival and climate change occurred simultaneously in many parts of the world," says Dr Nic Rawlence, lead author of the study and a postdoctoral research fellow from the Australian Centre for Ancient DNA and the University of Waikato.
"Using ancient DNA, radiocarbon dating and stable dietary isotope analysis, we have been able to show that before humans arrived, moa mitigated the effects of climate change by tracking their preferred habitat as it expanded, contracted and shifted during warming and cooling events.
"Moa were not in serious decline before humans arrived, as has been previously suggested, but had relatively stable population sizes."
Co-author of the Australian Research Council (ARC) grant-funded study, Dr Jamie Wood from Landcare Research, says the results show that "range shifts and minor population fluctuations observable in the fossil and genetic record are a natural response to environmental change and do not necessarily lead to extinction".