Ecologist and report author Manaia Permain-Fenton with a kakaruai. Photo: Supplied / Jo Monks
A population of South Island robin living near Dunedin is at risk of local extinction without intervention.
A recent study revealed a stark male-to-female ratio of 10-1 for kakaruai in Silver Stream, northwest of Dunedin.
University of Otago researcher and ecologist Manaia Permain-Fenton says it is a rare real-time look at the extinction process of a taonga.
Kakaruai used to be almost everywhere, but now there were only two wild populations on the east coast of the South Island, she said.
Loud calls from the males made it seem like they were more widespread at Silver Stream, but they were solo bachelors, Permain-Fenton said.
"In Silver Stream, there was only one female that I found that actually survived to the end of the season and that was despite going out there four or five times a week for about three months straight over the entire breeding season and I never found another female."
Predators - particularly rats - killed the birds and raided their nests, while deer and pigs destroyed their habitat and where they foraged.
There was no sustained predator control in Silver Stream, but she said a smaller scale intervention for a few years was making a difference before it ended.
It was a well-documented population dating back more than 100 years, and its decline was clear to see.
"To be able to see this population collapse in real time and to see records and the awareness of people knowing that this was coming and these warnings were made and yet it still happened," Permain-Fenton said.
A lot of people were not aware of the taonga's plight, she said.
Native species could not be saved without predator control and collaboration, she said.
"It's just not possible unless we work together and if we don't, we risk losing populations that we might not even realise that we have lost. These things can just disappear in silence, which is a real tragedy."
Ecosanctuary a lifeboat for the species
It has been more than a decade since two translocations of kakaruia from Silver Stream to Orokonui Ecosanctuary.
With no predators, lots of food and safe places to nest, the translocated kakaruia have thrived.
Advocacy lead Taylor Davies-Colley said they stopped counting when they got to 200 breeding pairs.
"Since that point, the numbers have increased to a point we're at now where people have described it as that they're dripping off the trees," he said.
Within a few hundred metres of track, he pointed out five kakaruai, including fledglings.
Kakaruia only have small home ranges, but he said they were probably at capacity at the ecosanctuary.
Each breeding pair might produce up to three chicks in a clutch and they could have two to three clutches in a breeding season.
"Where are all those chicks going? Why aren't there hundreds of kakaruia outside of Orokonui? How come when we walk around the forest outside the fence, why isn't it as rich in kakaruai as it is inside?
"And it's just because those birds are being set up for failure in a way by not having these outside environments predator free, these birds on the inside grow up in a naive environment, they go out there and it's just too easy. A cat or a stoat."
Davies-Colley said it was gutting to hear the kakaruia's plight at Silver Stream.
It meant the ecosanctuary was a lifeboat for the species, but they were only as secure as the ecosanctuary itself.
"That's still only one tiny little 307-hectare block of land with a fence around it. The more populations of these animals we can have, the more resilient they'll be but also we don't know what we're losing in terms of genetics."
Silver Stream is challenging and inaccessible terrain, which ramps up the costs and difficulty to maintain predator control.
Jacinta Steeds from Predator Free Dunedin said they were working nearby but their funding was to control mustelids and possums on a landscape scale and not site specific work.
"Currently, a best practice mustelid trapping network is being installed and this consists of over 100 double set DOC200 traps and this is being done by Te Rūnanga o Ōtākou's field team and the network will be in place before Christmas," Steeds said.
Predator Free Dunedin would support a group carrying out the rat control work at Silver Stream and could even provide traps.
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