In 1974, ornithologist Don Merton received approval for one final expedition into the mountains of Fiordland, New Zealand. His official task was to confirm that the kakapo, a large flightless parrot, had gone extinct. In the previous 25 years, the Wildlife Service had run 61 expeditions into the region and found only six birds, five of which had died.

Instead of evidence of extinction, Merton found 18 living kakapo. On another island, roughly 200 more were later located. The problem was that nearly all of them were male. The first confirmed female was not found until several years later. By 1995, only 51 kakapo remained.

New Zealand then launched a conservation program to save the species. All remaining birds were moved to predator-free islands, and every nest was closely monitored. The harder part of the rescue was still ahead.

The kakapo, known scientifically as Strigops habroptilus, is the largest parrot in the world. It is nocturnal, flightless, and can weigh up to 4 kg. It has a lifespan of up to 100 years. It breeds only once every few years, and only under specific conditions that researchers came to understand much later than they expected.

For around 60 million years, the kakapo lived in New Zealand without any mammalian predators. It never developed a fear of ground-dwelling animals because none existed. When humans introduced cats, rats, and stoats, the bird had no defense. The only reason it survived was that the most remote mountain valleys remained free of these predators longer than other areas.

It was in those valleys that Merton found the 18 birds between 1974 and 1977. All of them were male. A population of only males cannot reproduce. In 1977, the search moved to Stewart Island, 160 km to the south. There, the calls of around 200 birds were heard, but again, no females were immediately found.

In 1980, a dog led a guide to a female kakapo nestled between tree roots. She was smaller and greener than the males. Soon after, four more females were found with nests and chicks. The species could still breed, but the Stewart Island population was declining quickly because of feral cats.

Between 1980 and 1997, the birds were gradually moved to island sanctuaries. These birds became the foundation of the 1995 recovery program. Even under improved conditions, however, the birds did not breed as expected.

The idea of island protection was not new. It was first tried by naturalist Richard Henry in 1894. He transferred nearly 400 kakapo to Resolution Island. Within a few years, stoats swam across the channel and killed the entire population. Henry’s attempt failed.

The 1995 program chose islands farther from the mainland, cleared them of predators, and controlled the introduction of materials. One predator was not removed because it was not considered critical: rats. Rats did not attack adult birds, but they destroyed eggs and newly hatched chicks. They disrupted up to a third of all nesting attempts. Of the 12 chicks that hatched between 1980 and 1995 across three islands, only three survived.

The program protected nests from rats, but the birds still nested far too infrequently. Supplementary food was provided, including artificial pellets with nutrients. The birds ate and looked healthy, but they rarely nested.

Years of research followed. The kakapo does not breed on a seasonal schedule. It waits for a signal from a specific tree. The rimu, a New Zealand podocarp pine that can live for 500 years, produces a mass fruiting every two to six years. That fruiting is the trigger.

A female kakapo will not begin nesting until she has seen enough rimu fruit, regardless of what other food is available. For a long time, researchers assumed the bird was simply responding to abundant food. Providing other food in abundance did not produce the same result.

In 2015, researchers at Massey University found the reason. Rimu fruit contains 8.4 mg of calcium per gram of dry matter, which is necessary for egg formation and chick skeletal development. It also contains both forms of vitamin D, including D3, which was previously thought to come only from animal sources. Rimu synthesizes it. For a female forming eggs and raising a chick alone for months, this is a physiological trigger. Without it, nesting does not start. No artificial feed could replicate the effect because the mechanism was unknown.

What this meant was that in years when rimu did not fruit on a particular island, kakapo did not nest, no matter how much effort the program put in.

In 2002, rimu fruited heavily on Codfish Island for the first time in several seasons. The program decided to feed all females intensively to bring them into the best physical condition for nesting. More chicks were born, but 70% of them were male. In a species where males already outnumbered females, the program had worsened the imbalance.

The mechanism was evolutionary. Male kakapo are 30 to 40% larger than females and require more resources to grow. A better-fed female invests more in the costlier males. That works against a small population trying to recover.

The solution was to reduce feeding to a level where the female is healthy enough to nest but does not gain excess weight. At that level, the sex ratio returned to roughly 50/50. This was the first time the sex of an entire species’ chicks had been deliberately adjusted through changes to the mother’s diet. The population grew by 39% in the 2002 season.

From that point, the trajectory improved slowly. In years when rimu fruited, more chicks were born. The population crossed 100 individuals, then 150. By 2016, the population had doubled relative to 1995. Over the following six years, it doubled again.

The program sequenced the genomes of all living kakapo and some that had died. It was one of the first instances in which the genome of an entire species had been fully sequenced, not just a sample. The conclusion was that only 36 unique genetic lineages remained. For long-term survival through a population bottleneck, a minimum of 50 is needed. The kakapo was already below that threshold, and the missing genetic material no longer exists. The 51 birds of 1995 were all there was. All 236 alive today are their descendants.

Rangers are now managing evolution. Every pairing is planned against genetic records. Eggs are transferred between nests so that a female raises a chick with genetics as different from her own as possible. Some chicks are hand-reared and later returned to the natural environment.

The program’s equipment has moved beyond radio transmitters and notebooks. When a female settles on an egg, rangers sometimes replace it with a replica. The real egg is taken to an incubator with controlled temperature and humidity. The female continues to sit on the replica, which is made by Weta Workshop, the studio known for props for The Lord of the Rings. The replicas are 3D-printed, correctly weighted, and fitted with a speaker. At a certain stage, the egg begins to make sounds, preparing the female for the chick’s arrival. When the chick in the incubator reaches the right age, it is returned, and the female accepts it as her own.

Artificial incubation increases egg survival rates. Meanwhile, the female can recover and, in a rimu fruiting year, nest a second time. In 2019, 30 females nested twice. That contributed to a record 73 fledglings.

Every bird in the program is treated as an individual. This was demonstrated most visibly by Sirocco, a kakapo filmed by the BBC in 2009 attempting to mate with an ornithologist’s head. The video went viral. Sirocco was later appointed an official ambassador for the species and is the only kakapo permitted contact with humans. He is still alive and still behaves unpredictably.

The 2019 season was a success, but it was followed by an outbreak of aspergillosis on Codfish Island. A fungus present in most environments, aspergillus is normally managed by a healthy immune system, but kakapo, with their genetic bottleneck and dense nesting colonies, were vulnerable. Twenty-one birds were infected. Nine died, including females and chicks. The program evacuated 51 birds to the mainland for treatment in zoos and veterinary clinics. The outbreak was contained, but it showed that the entire population relies on a handful of islands and shares a common immunological vulnerability. A single pathogen on a single island could undo decades of work.

That is why the program began planning for a mainland presence, not as a return to the wild but as insurance. In 2023, 20 male kakapo were transferred to Sanctuary Mountain Maungatautari, a mainland reserve on the North Island protected by a predator-proof fence. It was the first time in more than a century that kakapo were on mainland New Zealand. Six of the first 10 birds climbed over the fence on their own. Kakapo climb with their beaks and claws, and the fence did not stop them. They were caught and returned. The fence was modified, and a second attempt was made.

In February 2026, the first chick in four years hatched on Pukenui Island. The rimu fruited at record levels that year, with 80 nests and 256 eggs. By April, 95 chicks had hatched, breaking the previous record of 73 fledglings from 2019. The Department of Conservation described it as the biggest season in recorded history.

The reason for the increase is in the numbers. In 1995, the program had 51 birds, 31 males and only 20 females. Decades of dietary management, genetic records, and planned pairings changed that. Today, there are 83 females of reproductive age, four times more than at the start.

The method of island protection developed for the kakapo is now applied on roughly 300 islands around the world. There have been 820 documented eradication operations across 666 islands, with an 88% success rate.

Richard Henry, the last kakapo from the Fiordland population, was found in 1975 and named after the naturalist who lost his birds to stoats in 1900. In 1998, he fathered three chicks. He died in December 2010 at approximately 80 years of age. Don Merton traveled to Codfish Island in November 2010 to say goodbye to him in person. Merton died four months later.

The current population includes 236 birds, each with a name, recorded weight, and genetic records. In January 2026, Deidre Vercoe, the program’s operations manager, said the goal is to create healthy, self-sustaining populations of kakapo that thrive, not merely survive. She said that with each successful season, the aim is to reduce the level of intensive, hands-on management. For 31 years, the program increased its control so the bird could survive. Its current goal is to reduce that control so the bird can live on its own.