Takahē famously came back from the dead. Once found around the country, they were hunted and predated to the point of invisibility, then presumed extinct for half a century before their rediscovery in Fiordland’s tussock-clad Murchison Mountains in 1948. Now, a palaeogenomics study shows just how close they came to oblivion.
The research, led by the University of Otago’s Alex Verry, analysed mitochondrial DNA from living takahē, from dead takahē collected in the 1800s, and from bones in museum collections, some up to 20,000 years old.
Previously, it was thought takahē had relatively high genetic diversity compared with some of our other endangered birds. This study paints a bleaker picture, showing a massive decline following the arrival of humans.
“The population bottleneck was way more drastic than we ever thought,” says co-author Nic Rawlence, an associate professor at the University of Otago.
The research shows that modern takahē, descended from those few Murchison Mountains birds, represent a tiny genetic subset of the pre-human takahē population—theirs is such an obscure lineage that the researchers didn’t find it in any of the pre-human bones.
“We’ve known for a long time that takahē must have undergone this big genetic decline,” says Verry. “But the fact that we can’t find that modern lineage shows just how drastic it was.”
That has severe implications for their future.
“When these populations get bottlenecked in small areas, with small population sizes, they become inbred,” says Rawlence. “Like a royal family, they marry their cousins and even their siblings.”
Lara Urban, a geneticist with the Technical University of Munich who was not involved in the study, points out that the research team only looked at mitochondrial DNA, which is easier to extract and sequence from ancient bones than nuclear DNA. “It would be interesting to see if the patterns of genetic variation hold on the nuclear genomic level,” she says.
Verry and Rawlence acknowledge that studying nuclear DNA, which they are in the process of doing, along with Urban, will yield a clearer picture. “You have a lot more information,” says Verry.
“Instead of having, say, one book on the biological heritage of takahē,” says Rawlence, “the nuclear genome has 50,000 books.”
Studying the nuclear genome of ancient takahē remains could reveal how badly the genetic bottleneck affects the birds in their daily lives—whether their immune systems are compromised, for example.
It wasn’t only the arrival of humans that affected takahē, the study shows. Using DNA from old bones to track genetic lineages through time, the researchers found that as the climate warmed after the last Ice Age, around 10,000 years ago, takahē expanded from refuges in the northwest South Island into eastern and southern parts of the South Island. Their old haunts, it seemed, became unsuitable. Takahē appear to have disappeared from the Nelson/Tasman region as forests and grasslands expanded.
That raises questions about where the birds prefer to live. Rawlence says that while takahē have often been regarded as a tussock grassland species, because they live in tussocks in Fiordland, that wasn’t always the case.
“The fossil record suggests they’re an edge species,” he says. “They like forest edges where the forest comes up against a frost flat or shrubland or a river.”
The findings highlight the importance of palaeontology and ancient DNA in making conservation decisions today. In 2018, takahē were reintroduced to Gouland Downs, an area of tussock grassland on the Heaphy Track in Kahurangi National Park, a decision made in part due to the presence of old takahē bones in caves there. But those bones, points out Rawlence, are from a completely different time and habitat, and the area might still be unsuitable for takahē.
“If you’re going to conserve takahē,” he says, “you need to take into account their fossil record and their prehistoric distribution and habitat preferences, which were very different to what we see today.”
So far, the Gouland Downs translocation has met with mixed success, but a slow start is typical in translocations of endangered species, says Glen Greaves, a senior takahē ranger at the Department of Conservation.
While habitat is an important consideration in choosing new homes for takahē, so is the number of introduced predators. Gouland Downs was chosen partly because predator numbers are relatively low there—and because DOC wanted to give takahē “a foothold in Kahurangi”. The hope is that the birds will eventually spread out into areas they like better.