Patterns of moa extinction inform modern bird conservation

A multidisciplinary team of researchers has leveraged a rich fossil record and cutting-edge computer modelling to recreate moa extinctions on Aotearoa New Zealand.

Understanding their behaviour can provide contemporary scientists with tools to conserve present day flightless birds under pressure from habitat loss.

Moas were a group of large flightless birds that went extinct 100-300 years after humans arrived in New Zealand in the mid-13^th century. For millions of years prior, there were nine species that ranged in size from slightly smaller than an emu to over two metres tall.  

Each of the moa species differed in reproductive rate, habitat preferences, dispersal ability, demographics, as well as the exact timing of their extinction.

The new study, published in Nature Ecology and Evolution, found that moas, despite their differences, converged on the same isolated refugia before going extinct.

“Our research overcame past logistical challenges to trace the population dynamics of six species of moa at resolutions not considered possible before,” says senior author Associate Professor Damien Fordham, from the University of Adelaide.

The sophisticated computer modelling used radiocarbon dated fossils, paleoclimate data, and archaeological insights to pinpoint the last holdouts for moas.

“They all contracted to cold, mountainous regions that were most distant from human colonisation,” says lead author Dr Sean Tomlinson, also from the University of Adelaide.

“By pinpointing the last populations of moa and comparing them with distributions of New Zealand’s living flightless birds, we found that these last havens shelter many of today’s persisting populations of takahē, weka and great spotted kiwi.”

While acknowledging that human impacts from Polynesian inhabitants differ from European colonisation, the research team argues that insights from moas can inform conservation of today’s endangered birds.

“The way [Polynesians and Europeans] expanded through New Zealand was very similar. They all colonised and altered the lowland ecosystems first,” says Tomlinson. “It’s important to understand the value of conserving these remote places that are still pristine or nearly pristine.”

As expected, the moa species with habitat preferences for these remote mountainous areas persisted the longest. But other moa species contracted to these refugia as well, suggesting that modern flightless birds are probably not living in their optimal habitat.

Tomlinson suggests that similar computer models could be used to “get a handle on where more robust populations were likely to have been, and maybe trying to restore and reinstate some of those populations.”

Flightless birds are necessarily limited in their dispersal. According to Tomlinson, computer modelling could “guide and even test conservation hypotheses before you go out onto the ground and translocate populations at huge expense.”

The computer models of moa populations were backed up by several different sources of data. First, the team only included fossils with high quality, “top shelf” dating.

Next, they used previously published data based on ancient DNA which used signs of inbreeding and genetic structuring to estimate population sizes. These data were used as benchmarks to validate the computer models’ population estimates.

Finally, co-author Atholl Anderson, a Maori scholar and archaeologist at the Australian National University and senior member of the Maori community, provided a valuable perspective on patterns of human impact.

“It was Atholl who could say, ‘that’s not how our communities operated. That’s not the way we would have explored the landscape,’” says Tomlinson. “All of our work would have been not just unethical but probably highly inaccurate as well without that perspective.”