A long time ago, there were 9 species of moa living in New Zealand, and they were the only birds found so far without wings, not even degenerate wings, the largest moa could grow to 3.6 meters tall, and the smallest bush moa was the size of a turkey. Before the Maori landed on the island, they were the largest terrestrial animals in New Zealand's forests, scrub and subalpine ecosystems, and they were completely extinct within 100 years after the arrival of humans.
And according to a new study recently published, an iconic moa species (eastern moa) experienced an existential crisis during the last ice age when they were infinitely close to extinction. But a small herd of moa survived in a small patch of forest on New Zealand's South Island, and when the climate began to warm, they quickly spread to the east coast and re-emerged.
What we know about this extraordinary story of survival has implications for how we can help living species adapt to climate change, and how we can protect and restore habitats that may be important in the future.
The eastern moa can grow to about 80 kilograms and nearly 2 meters tall, making it the smaller of nine extinct moa species. Fossilized fossils have been found in sand dunes, swamps, caves and central parts of the South Island, Otago, Canterbury and east Marlborough. Eastern moa rapidly became extinct due to over-hunting and habitat destruction by humans, as well as infestations by dogs and rats brought to the island by humans. But is the extinction of the eastern moa entirely due to human influence, or is it because of ancient climate change, which has already put them in a difficult situation, and the human influence only plays a "patching knife"?
Between 29,000 and 19,000 years ago, New Zealand was in an ice age, with glaciers much larger and more widely distributed than they are today, and as the climate became colder and drier, the distribution of grasslands and forests changed. Current climate change threatens the survival of many different species, as did climate change thousands of years ago. The fossil record suggests that the Ice Age was bad news for eastern moa, as bones from eastern moa from this period are rarely found.
But the lack of fossils doesn't necessarily mean that a species's survival is difficult. Maybe they just avoided caves and swamps, and somewhere else we might end up finding their bones. To learn more, the researchers sequenced dna from dozens of eastern moa skeletons to understand how their genetic diversity and population size have changed over the past 30,000 years.
Large healthy animal populations tend to have higher genetic diversity, while lower genetic diversity may be a sign of population decline. The researchers found that after the last ice age, the genetic diversity of eastern moa was low. So, eastern moa didn't cope well with the ice age climate, but how did they manage to escape extinction? The new study provides a clue: Their genetic diversity is highest at the southernmost tip of the South Island.
During the Ice Age, grasslands in many areas replaced moist forests, which were the favorite habitats of eastern moa birds, which may explain why they struggled to survive. Fortunately for the eastern moa, however, during this time a small forest in southern New Zealand survived, on which moa struggled to reproduce.
Scientists have a special name for habitats where species are sheltered and endure climate change — "sanctuaries." Once the climate begins to return to its pre-ice age state, eastern moa are able to return to parts of the area they previously occupied. Their numbers have rebounded well, and they are the most common moa in some parts of New Zealand when Maori arrive in New Zealand.
Ancient DNA from fossils from around the world suggests that sanctuaries play an important role in adapting species to climate change. The story of the eastern moa shows that the same is true of New Zealand. But importantly, eastern moa are affected differently than other moa, suggesting that not all species are affected by climate change in the same way. The study highlights that given that habitats of certain species are currently found to be unsuitable for their survival in the near future, there is a need to conserve and restore a wide variety of habitats in the future.
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