The science behind the remarkable kōkako recovery
One of New Zealand’s most successful conservation programmes is in full flight
Deep in New Zealand’s ancient Pureora rainforest, a small group of North Island kōkako catchers wait in the dark, eager to coerce a pair of the wild forest-dwelling birds into their net.
It’s 6.30 am and the winter sun is starting to peek through the branches of the forest's tall podocarp trees. The group, made up of a conservation ecologist and four conservation volunteers, work around a large fallen log to secure their 10-metre high mist-net. The net hangs perfectly, belayed to surrounding trees, where it’s known a pair of the beloved songbirds are close by.
An hour earlier, the group had hiked about three kilometers from the edge of the protected central North Island forest through thick native bush to their marked catch site. It’s a brisk, clear morning and, with the group clothed in beanies and balaclavas, the scene appears more like a group of bandits ready for a swift attack, than a calculated recovery operation. .
The large blue-grey songbird with a distinctive vibrant blue wattle, long strong legs, and rounded wings is a territorial species with a unique and impressive song.
Kōkako prefer to run along branches rather than fly, so to lure a bird to fly into the net conservation ecologist Dave Bryden has pre-recorded the male bird’s song and begins playing the recording back through a speaker system to encourage the bird to investigate or challenge the attractive call.
This morning’s venture comes off the back of a successful week for the group. They’ve already caught eight of their nine quota limit from the ‘source’ site, where birds have been well-established and can be harvested.
Once caught, the birds are relocated to a predator-controlled forest suitable for establishing new populations of the species. For these kōkako caught in Pureora, that means being driven to their new home two hours away in the protected Pirongia Forest Park from where they are descendants but have not been heard in decades.
The group is eager to catch their last bird to reach their quota and move on to their next location further north tomorrow, but there’s only a small window from dawn to catch while the birds are active.
As the recording plays, the young male kōkako is intrigued. He leaps from high in the podocarp tree to investigate but soars over the net – a missed attempt. Repositioning the speakers, Bryden lures the kōkako over again and a catch occurs. Bryden and the group assemble – quickly but carefully lowering the net and freeing the bird.
Once caught, each bird is weighed, banded, measured, blood-tested, and feather-sampled for genetic identification, before being put into a box and translocated to its new home. It’s a quick and well-rehearsed procedure for the group as they have to work within a 2-hour window of catching and releasing a bird.
Today’s early morning catch falls within a wider catch-and-release kōkako recovery programme administered by the Government’s Department of Conservation (DOC).
Kōkako belong to the endemic New Zealand wattlebirds and are one of the country’s many birds that have borne the brunt of decades of predators running rampant through native forests, raiding nests and destroying habitat. By the late ’90s kōkako breeding pairs were down to just 330.
Recovery of the species stems from years of scientific research spurred on by conservation groups, researching kōkako habits and movements to determine the cause of their decline.
In the late ’80s wildlife ecologist, John Innes became involved, tracking and analyzing the movements of kōkako, and learning about their fragile life.
“I started working at a time when these populations were disappearing one by one around the central North Island, but there were still a few big populations left,” says Innes.
“To me this raised a huge number of puzzles about why they were disappearing from forests that were often legally protected and unlogged. This was the science question: what was causing these birds to go?”
Just before Innes’s research a study had been undertaken of kōkako in relation to the now famous logging controversy in Pureora. The study blew open the basic biology of kōkako.
“From this it was found kōkako were territorial, they sang from treetops, lived in pairs and, interestingly, some of them were not trying to nest and some were trying but failing – so we picked up the research from that point and my first work was to look at the survival of these kōkako populations and research the cause of decline,” Innes explains.
“We followed birds, banded them, found their nests, and tracked the fate of those nests. The outcome was that the birds that were not trying to nest both turned out to be males as the female birds were being killed at the nest.”
Through the very early use of time-lapse video cameras, researchers discovered that possums and ship rats were to blame and were constantly harassing nests. This was a remarkable discovery for New Zealand.
“We found that night after night up trees and hidden to humans, in this kind of invisible way, those animals were plundering bird nests,” he says.
During this time researchers discovered it takes 3 weeks to hatch a kōkako egg and 4 weeks to raise a chick, but with the number of predators dramatically outnumbering kōkako and the ancient species not knowing how to defend their nests, they were heading towards a rapid decline and extinction.
“There were 4 to 7 ship rats and 4 to 7 possums per hectare, and night after night they were raiding those nests, so we knew the solution lay in introducing pest control.”
“We had transmitters on some birds and bands on others, so we learned both how to find nests and about the behavior of males and females when they were nesting. When a nest site was located, we would watch it and see what stage they were at,” he says.
“We would climb to nests, and we knew that if we had a fair idea of when eggs were laid then we should have a fair idea when eggs should hatch. If the hatching had somehow failed – and especially if we had filmed a failure – we would gather remains of eggs and were able to recognize what an eggshell looked like when it had been eaten by a possum or a rat.”
At the same time, the team began experimental pest control programmes – targeting ship rats and possums in large areas.
“It was a really audacious thing to try and control rats in forests – people thought we were crazy and it just seemed impossible,” admitted Innes. “But over the following 7 years we turned that pest control on and off in different places and measured kōkako nesting success along with the number of adults. And the truth came out: no, you can’t save all nests, but you can save enough to increase nest success to a level where some chicks survive well and then recruit to the adult population.”
While predator control was tested in some areas, the remaining unmanaged populations simply disappeared.
Through pest control, the populations grew and the research of Innes and others was the beginning of the kōkako recovery programme, coordinated by DOC. After 30 years of research, the conservationists are now on their third recovery plan, which involves collating the best science and tools for kōkako recovery.
Pirongia Te Aroaro o Kahu Restoration Society Chair Clare St Pierre points to the kōkako release site within the predator-controlled forest
Today there are around 1,700 breeding kōkako pairs in New Zealand. While the future of this bird is conservation-dependent, there are now 11 relict and 14 translocated populations on the mainland and offshore islands and the birds have gone from ‘Nationally Critical’ to ‘At-Risk – recovering’.
The Recovery Group sees large, growing, relict populations as the ‘capital’ from which ‘interest’ can be harvested.
Today, more than half of the kōkako populations are managed by community groups working with DOC to implement the recovery programme. Year after year conservationists will undertake pest control and translocations to ensure this beloved songbird species recovers and remains in New Zealand forests. As Innes says, “If you die without hearing the song of a kōkako in a New Zealand forest – you die poor.”
Identifying ship rats and possums as key agents of decline and treating pest management as an experiment through this kōkako research has been instrumental for the conservation of many New Zealand birds.
This research has been referred to as one of the most successful conservation stories of a New Zealand bird species. In 2017, John Innes was awarded a lifetime achievement by Science New Zealand in recognition of his contribution.
The research was funded by the Department of Conservation and public good science funds via the NZ Forest Research Institute (1980–1991), and Manaaki Whenua - Landcare Research (1992 onwards).
Story by Suzette Howe Photography by Jonathan Smit & Suzette Howe
Department of Conservation
Pirongia Te Aroaro o Kahu Restoration Society