There are two things you need to know about New Zealand: It’s impossibly green, and you can't throw a rock without hitting a sheep (don't actually throw rocks at sheep, it's just a figure of speech). The place is lousy with them, and for that you can thank Captain Cook, who introduced them in 1773. It was just one of the many mammals humans have brought to New Zealand, which has historically had zero mammals other than bats. Now, they’re everywhere—rats, cats, dogs, and about eleventy million sheep.

And it’s an ecological nightmare. Rats eat eggs and cats eat birds, and the endemic wildlife is suffering for it. Almost half of New Zealand’s native bird species are now extinct, while a particularly bizarre bird is teetering on the edge: the kakapo. It is the world's only flightless parrot. It can live 100 years. Its sex life is best described as ... involved. And there are just 126 left in the wild. But those 126 birds have guardians, dedicated rangers who’ve sequestered them on three small mammal-free islands, tracking them and feeding them and slowly, ever so slowly, boosting their numbers.

Back in the 19th century, New Zealand was positively swarming with kakapo, according to biologist Andrew Digby of New Zealand’s Department of Conservation. Hundreds of thousands of them, perhaps millions. “With early European explorers in the 1800s,” he says, “there's records of them saying that they'd have a dozen of them land in their camp at night and make so much noise that they couldn't sleep. They used to say they'd catch them just by shaking a tree, and then they'd get a couple of birds falling out.”

But the introduced mammalian predators have been pecking away at the kakapo’s numbers, until in the 1970s scientists feared only a population of males was left—not exactly good news for a species. But another population of kakapo, with females, was soon found on Stewart Island at the southern tip of New Zealand. Thus the kakapo was saved, but its numbers continued dwindling until hitting their lowest in the mid-1990s: 50. Ever since, though, conservation efforts have slowly but surely been bringing the kakapo back.

Feeding kakapo does two things: Gives them energy for the mating season and results in hilarious pictures. Andrew Digby/New Zealand Department of Conservation

So why are kakapo so vulnerable to mammals? Well, they’d evolved over 18 million years without having the furry things around. They took up the terrestrial life because, simply put, they could. They blend in well with the undergrowth and there were no mammalian predators stalking about in search of eggs, so it made sense to give up flight, which is highly energy intensive. It’s among the many illustrations that there’s no such thing as “progress” in evolution. Sure, flight was an impressive achievement in the history of life on Earth, but if it no longer behooves a species to fly, it can be better to evolve it away. Unfortunately for a kakapo, the introduction of mammals made this evolutionary path rather problematic.

Counterintuitively, the kakapo actually has relatively huge wings for a flightless bird (its flightless counterpart in New Zealand, the kiwi, has wings that have almost disappeared entirely), which it uses to glide out of trees—or, more accurately, awkwardly tumble out of them. Kakapo are accomplished climbers, using their talons and beak to make their way as much as 100 feet up into the canopy in search of berries. “And sometimes in the summer when the females are breeding they're in such a hurry, they need to get the food back to their chicks as quickly as possible,” Digby says. “So rather than climbing back down they'll just jump off from high up in the tree. They're tens of meters up, and they'll sort of crash to the ground.”

Andrew Digby/New Zealand Department of Conservation

Indeed, scientists will find them injured from such stunts—but it’s worth it for the birds to get back and protect their young ‘uns from things like owls (which are too small to go after adult kakapo). There is much at stake here, and not just because the species is in trouble, but because kakapo only mate every three years. This coincides with the fruiting of the rimu tree, which produces the caloric energy that fuels the kakapo’s bizarre mating ritual.

Which goes as follows. Toward the end of the year, right around Christmas, male kakapo ascend hills all around the three islands they call home. Here they build networks known as “tracks and bowls,” which are, as you’d expect, depressions that the males scrape out of the dirt and connect with trails. Every night they sit in these bowls, puffing themselves up and booming an unexpectedly deep sound that can travel more than four miles. The males will do this for eight hours a night for months on end, booming booming booming, to attract females, who will mate with suitable fellas for up to 45 minutes a go. (A kakapo has also mated on at least one occasion with the head of a BBC presenter, as you can see below.) “So it's a pretty unusual mating system,” Digby says. “And this booming noise is kind of weird. You feel it in your stomach. It’s not just hearing it, it’s just a really, really low frequency.”

Females will typically lay a single egg—just one egg every three years. The good news is that kakapo may live for up to a century, making for a whole lot of breeding seasons. The bad news is that when you have such small populations, inbreeding is inevitable.

This is where the rangers come in.

An artificial insemination of a kakapo. Andrew Digby/New Zealand Department of Conservation

Humans Cleaning Up Human Messes

The Department of Conservation's four permanent rangers, who rotate between the three kakapo islands, are obsessively monitoring the 126 remaining birds. Transmitters tell them not only where each bird is, but who is mating with whom. “So we want to make sure that we don't have birds too closely related that are mating with each other,” Digby says. “Brothers and sisters, that sort of stuff.”

They’ll also preempt the birds by artificially inseminating them, because inbreeding can severely lower the fertility of female kakapo. Plus, genetic diversity in general is pivotal in any population, and especially so in such a small one. Genetic diversity means healthy variation among animals, and healthy variation allows a species to better adapt to its environment. Those with advantageous variations survive to mate and pass the genes responsible for them along, while their less fit peers perish, helping the species adapt. Plus variation means a species can better handle outbreaks of disease: Some individuals will be better equipped to fight it and pass down those convenient genes. If a population is inbred, though, it may be that none of the individuals can fight it.

Kakapo chicks. New Zealand Dept. of Conservation

Accordingly, an outbreak among kakapos could be devastating. So their islands are under strict biocontrol. Not only are visitors’ bags checked for rats and mice, but everything is sprayed with disinfectant to snuff out any diseases.

However precarious the kakapo’s existence may be, so far the program seems to be working. More birds are being born than are dying, so the population is growing, and Digby is realistically optimistic.

“Some years when we don't have breeding and birds die, then we'll make a net loss,” he says. “But overall we're making a net gain, but only a net gain of a few birds a year. We're slowly, slowly getting there.”

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