Human settlement of islands across the Pacific Ocean was followed by waves of faunal extinctions that occurred so rapidly that their dynamics are difficult to reconstruct in space and time. These extinctions included large, wingless birds called moa that were endemic to New Zealand. In a new study, scientists from the University of Adelaide and elsewhere reconstructed the range and extinction dynamics of six moa species across New Zealand. They found that the final populations of all moa species persisted in cold, mountainous areas that were generally last and least impacted by people. They also found that these refugia for the last populations of moa continue to serve as isolated sanctuaries for New Zealand’s flightless birds.
This is an artist’s impression of the Upland Moa, Megalapteryx didinus, by George Edward Lodge, 1907.
“Our research overcame past logistical challenges to trace the population dynamics of six species of moa at resolutions not considered possible before,” said University of Adelaide’s Dr. Damien Fordham.
“We did this by combining sophisticated computational models with extensive fossil records, paleoclimate information, and innovative reconstructions of colonization and expansion of people across New Zealand.”
“Our research shows that despite large differences in the ecology, demography and timing of extinction of moa species, their distributions collapsed and converged on the same areas on New Zealand’s North and South Islands.”
Dr. Fordham and colleagues found that the final populations of all moa species persisted in the same isolated, cold, mountainous environments that today harbor many of the last populations of New Zealand’s most threatened flightless birds. These include Mount Aspiring on the South Island, and the Ruahine Range on the North Island.
The Haast’s eagle (Hieraaetus moorei) attacking two moas. Image credit: John Megahan / PLoS Biology, doi: 10.1371/journal.pbio.0030020.
“Populations of moa are likely to have disappeared first from the highest quality lowland habitats that Polynesian colonists preferred, with rates of population declines decreasing with elevation and distance traveled inland,” said 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.”
“What’s more, these ancient refugia for moa overlap with the last mainland populations of the critically threatened kākāpō.”
“Although recent drivers of decline of New Zealand’s native flightless birds are different from those that caused the ancient extinctions of moa, this research shows that their spatial dynamics remain similar.”
Moa browsed trees and shrubs within the forest understorey. Image credit: Heinrich Harder.
“The key commonality among past and current refugia is not that they are optimal habitats for flightless birds, but that they continue to be the last and least impacted by humanity,” said Dr. Jamie Wood, also from the University of Adelaide.
“Like earlier waves of Polynesian expansion, habitat conversion by Europeans across New Zealand, and the spread of the animals they brought, was directional, progressing from lowland sites to the less hospitable, cold, mountainous regions.”
The team’s results appear in the journal Nature Ecology & Evolution.
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S. Tomlinson et al. Ecological dynamics of moa extinctions reveal convergent refugia that today harbour flightless birds. Nat Ecol Evol, published online July 24, 2024; doi: 10.1038/s41559-024-02449-x
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