Lost giant: What scientists just learned about the moa’s demise

Scientists have reconstructed the demise of Aotearoa’s long-lost moa to find lessons they say might help save species remaining today. Image / Paul Martinson

Scientists have reconstructed the demise of Aotearoa’s long-lost moa to find lessons they say might help save species remaining today.

This year, researchers reported how our endangered flightless birds are taking refuge in areas where six species of moa last lived before they were hunted to extinction from the 13th century onward.

Now, they’ve taken a closer look at whether conservation measures like “no take” zones might have helped moa survive, showing these reserves would’ve likely been required across areas spanning roughly half the country.

“That’s more land than is currently covered by conservation covenants in New Zealand,” said Dr Sean Tomlinson, who led the study while based at Australia’s University of Adelaide.

Even with modern conservation methods and objectives, Tomlinson said it might have been “impossible” to detect the rates of decline and develop meaningful measures to save them.

In the study, published online ahead of peer review, Tomlinson and his New Zealand, Australian and US colleagues drew on the moa’s rich fossil record to develop simulation models that estimated birth rates, deaths and migrations for each species.

They also accounted for the increasing human population’s hunting pressure, as well as local climates and environments.

Haast's eagle attacking two moa, which lacked other large predators before the arrival of human settlers in Aotearoa. Illustration / John Megahan

With those models, the researchers ran thousands of plausible simulations to pinpoint the versions that best matched the fossil record, while also testing alternative realties called “counter-factual scenarios”.

The results suggested not all moa species were equally targeted in hunting, nor did they all die out around the same time - with some vanishing within a century of human arrival, and others holding on for several hundred years.

While larger species, such as giant moa, were hunted at nearly twice the rate of smaller species, they weren’t the first to disappear, as their extensive distribution and higher population numbers likely bought them more time.

Smaller species like Mantell’s moa, or moa ruarangi, with their limited range and lower reproductive potential, were among the first to go.

The study also noted other factors that worked against moa, which had roamed Aotearoa’s prehistoric wilderness for millions of years, largely free of predators.

They matured late, reproduced infrequently and had high adult survival rates.

The study found even a minimal harvest rate - accounting for less than 6% of the population annually - could have led to extinction within 95 to 315 years, depending on the species.

For birds that took several years to reach maturity and laid few eggs each year, the researchers found even small, sustained harvesting was enough to seal their fate.

“Basically, moa were probably not resilient to anything that increased adult mortality, and this likely reflects their evolution in isolation, away from predators " said Associate Professor Damien Fordham from the University of Adelaide’s Environment Institute.

Among Aotearoa's species of extinct moa, females were more than twice the size of males.

“The study wasn’t about assigning blame to Aotearoa’s earliest settlers, describing the moa’s extinction as just one part of a global phenomenon.

“When humans first arrive in any ecosystem, huge ecological changes tended to result - including species extinctions.”

“What our study shows is that it would be very difficult for moa and humans to have coexisted because even low levels of subsistence harvesting were not sustainable.”

Tomlinson said one of the biggest lessons from this and previous research was that protecting remote, rugged wildernesses and keeping them as pristine as possible was critical for preventing extinctions, not just in New Zealand but globally.

But that alone wouldn’t be enough.

“To successfully reverse threats to biodiversity, we also need to restore habitats that we have damaged and start returning these iconic, threatened species back to the landscape in optimum habitats where they used to be,” he added.

“Our research shows that these areas are going to need to be large, particularly for big animals that grow and mature slowly. But if we don’t come to grips with this ... we’re probably not going to reverse the current downward spiral in biodiversity.”

The study findings also left some other intriguing questions to answer.

“My biggest curiosity now focuses on the ecological consequences of moa extinctions,” Tomlinson said.

“For example, Haast’s eagle has long been thought to have gone extinct soon after moa did because moa were their primary prey.

“I’m really curious to know whether we could use our modelling approach to determine whether the demise of moa caused co-extinctions.”

Tomlinson said it’d been critical to ensure the new research was consistent with mātauranga Māori [Māori knowledge] and concepts of kaitiakitanga [guardianship]

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.

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