How did ancient moa survive the Ice Age – and what can they teach us about modern climate change?

An iconic species of moa was nearly wiped out during the last Ice Age, according to recently published research. But a small population survived in a modest patch of forest deep in New Zealand’s South Island and quickly spread to its east coast once the climate began to warm.

What we learn from this remarkable survival story has implications for how we can help living species adapt to climate change, and how we conserve and restore what could be important future habitats.

Able to reach around 80 kg and up to 1.8 meters in height, the eastern moa was one of the smallest of the nine extinct species of moa. It takes its name from the fact that its fossil bones have been found in sand dunes, swamps, caves and mounds all along the eastern parts of the South Island – Southland, Otago, Canterbury and Marlborough.

The eastern moa became extinct due to overhunting and habitat destruction by humans, and maybe predation by kurī (dogs) and kiore (rats). But were eastern moa populations thriving when people arrived, or were they already struggling due to ancient climate change?

Skull of an eastern moa. Genetic information can be obtained from moa bones even after thousands of years. Te Papa CC BY-NC-ND 4.0.

Refuge in the south

Between 29,000 and 19,000 years ago, New Zealand was in the throes of an ice age. The glaciers were much larger and more extensive than they are today, and the distribution of grasslands and forests changed as the climate became colder and drier.

Today’s climate change threatens the survival of many different species, and so was climate change thousands of years ago. The fossil record suggests that the Ice Age was bad news for the eastern moa, as few eastern moa bones from this period have been discovered.

But a lack of fossils doesn’t necessarily mean a species was having a hard time. Perhaps they simply avoided the caves and swamps where we might eventually discover their bones.

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To find out more, we sequenced the DNA of dozens of eastern moa bones to see how their genetic diversity and population size have changed over the past 30,000 years.

Large, healthy animal populations tend to have high genetic diversity, while low genetic diversity can be a sign that a population is in decline. We found that the eastern moa had very low genetic diversity immediately after the last ice age.

So eastern moa didn’t hold up well to the Ice Age climate – but how did they manage to escape extinction? Our study gives a clue: their genetic diversity was highest in the far south of the South Island.

The Rimu were predominant in the podocarp forests which the eastern moa preferred. The distribution of these forests changed dramatically during the Ice Age.
Katja Schulz/Flickr CC-BY 2.0

Preserve future habitats

During the Ice Age, grasslands replaced moist podocarp forests in many areas. These forests were the eastern moa’s favorite habitat, which may explain why they struggled to survive.

Fortunately for the eastern moa, however, small pockets of forest have survived in southern New Zealand at that time. While the eastern moa have disappeared from most of the country, our study suggests that they hung on in the remnant forest in the far south of the South Island.

Scientists have a special name for pockets of habitat where species can find shelter and endure climate change – ‘refuge’.

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Once the climate began to return to pre-ice age conditions, the eastern moa were able to return to the parts of the country they previously occupied. They rebounded so well that they were the most common moa in parts of New Zealand by the time the Polynesians arrived.

Ancient DNA from fossils around the world has shown that refugia play an important role in enabling species to adapt to climate change. The history of the eastern moa shows that this is also true in New Zealand.

Importantly, the eastern moa was affected differently than other moa, showing that not all species are affected by climate change in the same way. Our study underscores the need to conserve and restore a diverse range of habitats for the future, as the places where the species are found today may not be suitable for them in the very near future.

By ensuring that species can continue to find suitable refuges, we can reduce the number of those that go extinct due to our global impacts on climate.

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