New Zealand was once home to giant, flightless birds known as moa, which had evolved in an environment free of natural predators. However, the arrival of humans in the mid-13th century posed an unprecedented threat to their survival.
The moa, unprepared for even moderate hunting pressure, could not withstand the onslaught brought by humans. All nine species of moa were driven to extinction shortly after first contact. The rapid disappearance of these birds made it difficult to trace their decline—until now.
Our recent research has provided new insights into how moa populations dwindled and ultimately vanished. We reconstructed the decline, range reduction, and extinction patterns of six moa species by simulating their interactions with humans and their environment across hundreds of thousands of scenarios. We then validated these simulations with fossil data.
Our findings reveal that all six moa species eventually retreated to the cold, remote mountains of New Zealand’s North and South Islands. Interestingly, these same mountainous areas are now the last refuge for New Zealand’s remaining flightless birds.
The Impact of Human Expansion on Island Biodiversity
Oceanic islands are renowned for their extraordinary biodiversity, showcasing some of Earth’s most unusual evolutionary adaptations. These islands are home to everything from tree-sized daisies to miniature elephants and numerous flightless birds.
However, islands also face severe extinction risks, particularly in the Pacific, where human impact has been especially devastating. The Pacific islands were among the last regions to be settled and transformed by humans.
Human migration across the Pacific began around 4,000 years ago with remarkable sea voyages originating from Taiwan. These early explorers first journeyed south to the Philippines before venturing onto some of the most remote islands on Earth.
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Such voyages required advanced seafaring technology and navigational expertise to traverse vast expanses of open ocean.
The final stage of these migrations saw the settlement of central and eastern Polynesia, culminating in the colonization of the New Zealand Archipelago by Polynesians—ancestors of the Māori—in the mid-13th century.
Upon arrival, humans ignited fires, hunted native animals, and introduced invasive species, including Pacific rats. As a result, New Zealand’s unique ecosystems suffered one of the most severe and rapid declines in native wildlife across the Pacific.
Patterns of Moa Extinctions and Range Collapse
Moa went extinct within three centuries of human arrival in New Zealand, but their disappearance wasn’t instantaneous.
Our research indicates that Mantell’s moa was the first to vanish, disappearing within just 100 years of human contact. Almost a century would pass before other moa species began to go extinct.
Mantell’s moa was particularly susceptible to extinction due to its slow population growth. Even minimal but consistent hunting was enough to outpace its reproductive capabilities, leading to its rapid decline.
Other moa species demonstrated slightly greater resilience. They benefited from traits such as higher growth rates, larger ranges, more substantial populations, or the ability to thrive at higher altitudes, away from human encroachment.
The stout-legged moa, for instance, survived the longest, eventually disappearing about three centuries after humans arrived.
Our study reveals that moa initially disappeared from high-quality lowland habitats, which were the most attractive to early settlers. As moa populations declined, the remaining birds retreated to higher altitudes and more remote areas.
Contrary to previous beliefs, which suggested that species under pressure would contract to their optimal or preferred habitats, our findings show that moa moved as far away from human activity as possible, rather than just shifting to less ideal environments.
Insights from Moa Extinctions: Lessons for Today’s Flightless Birds
Our research has also examined the distribution of New Zealand’s remaining flightless birds.
It appears that the ancient refuges of moa now host populations of critically endangered native flightless species, such as the takahē, weka, and great spotted kiwi. These moa refuges also served as the last known habitats for the critically endangered kākāpō.
These areas, while no longer ideal for moa, continue to provide crucial sanctuary for today’s flightless birds. They remain among the most isolated and least impacted by human activity.
Although current conservation efforts have prevented the extinction of New Zealand’s remaining flightless birds, they still face threats related to human activity. Habitat loss and the effects of invasive species, following European settlement, have extended from lowland areas to the more challenging, cold, and mountainous regions.
The historical decline of the moa underscores the critical importance of preserving these remote, relatively undisturbed areas. To avert future extinctions, we must prioritize the protection of these wild places. Our research also provides valuable insights into understanding past extinctions, particularly on islands where fossil and archaeological records are sparse.
(Includes inputs from online sources)
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