Life will find a way
We cull hybrids. We steal their eggs, and break up inter-species breeding pairs, all in the name of genetic integrity. Protecting the mauri. We created this tangle by bringing in exotic species. Can we ever undo it? And should we even try?
Perhaps, if I were to choose a snapshot that represented wild New Zealand in the 21st century, this would be it. It’s a peaceful lake on the southeast coast of the South Island, surrounded by cabbage trees, flaxes and tussocks that dip their tillers in its placid waters. A brisk stream, full of trout, runs alongside, while kōwhai trees on the hill above shudder with tūī and bellbirds.
The lake is crowded with gulls and waterfowl that have little fear of humans. In fact, they clamber up on the lake edge in the hope of being fed. This lake, you see, is not tucked away in some virgin rainforest, or hidden in a remote corner of the mountains. It’s the duck pond at Dunedin’s Botanic Garden.
Amid Monday-morning toddlers, a rabble of ducks gather on the concrete that encircles the lake. At a glance, these seem like your standard, picture-book ducks—the females mottled grey with a dark stripe across the eye and a shimmering green-blue panel on the wing, the males sporting an iridescent green head and a white neck band.
They look like the waterfowl of a half-remembered Britain; bit characters out of The Wind in the Willows, perhaps. But these ducks are actually among New Zealand’s most critically endangered birds. Well, sort of. It’s a long story.
At the centre of this tale are two closely related ducks, separated for millions of years by the world’s oceans, but brought together by the currents of human history.
The New Zealand grey duck (Anas superciliosa superciliosa), known to Māori as the pārera, is a subspecies of a duck found across Australia and the South Pacific, the product of a long, isolated evolution at the southern edge of the world.
The mallard is one of the world’s most common ducks. Widespread across Europe and North America, it has been shaped by tens of thousands of years of close proximity to humans. It is the species from which most of our barnyard ducks have been domesticated.
Grey ducks once flocked in their millions on the waterways of Aotearoa. For a number of iwi and hapū, they are a taonga species.
As well as valuable resources, these species are kin, whose wellbeing, whakapapa and mauri—their integrity—people have a responsibility to protect.
In pre-European times, Māori would venture into the land’s interior to harvest them. “They were hunted particularly during the moulting period in the spring,” says Ngāi Tahu kaumātua Edward Ellison. “They would be driven ashore and captured. The pārera would have been an important part of the traditional diet, given their numbers and ease of catching.”
Explains Victoria University ecologist Murray Williams: “They were the only duck of large lakes and estuaries in New Zealand. On all the ephemeral wetlands, lagoons, lakes, and up rivers—that’s where the grey duck would have been.”
Like all our native birds, the grey duck was well adapted to New Zealand’s heavily forested environment. By the early part of the 20th century, though, the destruction of that forest had already set the species’ decline in motion.
“Most of New Zealand was going up in smoke,” says Williams. “There was a lot of land clearance. So the rivers and lakes were becoming bare on the margins.
“Hunters whose bags used to be 50 a day were complaining that [grey ducks] now weren’t so common. They wanted more sporting birds.”
Enter Cecil Whitney, a successful Auckland businessman and prominent member of the Acclimatisation Society, which at the time was busy stocking New Zealand with introduced species, from deer and geese to salmon and trout.
Whitney’s passion (some might say obsession) was the mallard. With almost religious zeal, he set about importing and breeding mallards from gamebird farms in Europe and distributing their eggs around the country.
“Hundreds of eggs were given to farmers, who raised them under chooks,” says Williams. “They’d just open the coop after the bantams had hatched them and let them go.”
Whitney’s drive to fill our waterways with his beloved mallards was almost unstoppable. “He basically forced societies all over New Zealand to breed them,” says Williams. “He had the ear of the Minister of Internal Affairs, who effectively told his department to set up a game farm and breed the bloody things. Which they did.”
In the end, something like 30,000 mallards were liberated in New Zealand. They were protected from hunting while their natural predators—hawks and eels, also taonga species—were systematically exterminated.
“The thinking was very short term,” says Aroha Mead (Ngāti Awa, Ngāti Porou), a specialist in intellectual property, biosecurity and indigenous bioethics, “and narrowly focused on the gains of one stakeholder.”
Where mallards and grey ducks shared the same waterways, a phenomenon was observed that would soon have an enormous bearing on both ducks’ futures.
“Right from the very beginning,” says Williams, “there were people who were saying, ‘I just found a bird that looks like a cross between the two.’”
Be it the Minotaur, swinging his bullish head in the Labyrinth of Greek mythology, or Kurangaituku, the fearsome bird-woman of Māori lore, the hybrid bothers our subconscious. On a fundamental level, there is something unsettling to us about the joining of one species to another. Something unnatural.
And yet, biology begs to differ. Modern genetic techniques allow scientists to peer into the DNA of animals and plants, where they often find evidence of hybridisation. Hybridisation, we now know, is happening all the time. Over 25 per cent of plants are known to hybridise and it’s now thought that at least 10 per cent of animals do as well.
Scientists have even discovered that we humans are a kind of hybrid. When our ancestors migrated out of Africa, they encountered another hominid species, the Neanderthals, living in Europe.
Before the Neanderthals went extinct, our ancestors bred with them. Not on one or two isolated occasions but often, over a long period of time. When the hybrid offspring of those unions reproduced with humans (a process known as back-crossing), the Neanderthal genes they carried were embedded into the human genome.
As a result of back-crossing, around two per cent of the non-African human genome is now made up of Neanderthal DNA.
Such discoveries are not comforting for the taxonomist, whose unenviable (and ultimately futile) task is to fit the world’s species into solid, clearly defined boxes. If a plant or animal’s genome contains genes from other species, where does one species start and the other finish? How can you even define a species if genetic material can flow so readily from one to another?
Hybridisation may in fact be a fundamental driving force of evolution. In circumstances where climate is changing, new habitats are opening up, or when disease is rampant, the injection of new genetic material through hybrid pairings may bolster or even save a species.
The introgression of Neanderthal genes may have helped our ancestors survive the cold, arid climate of Pleistocene Europe. It has also left us with some genetic baggage we could probably do without. Crohn’s disease, for example, is thought to have come to us through the Neanderthal line. Such is the genetic lottery of hybridisation.
A place where two species breed together is known as a hybrid zone. Fifty thousand years ago, Europe was a hybrid zone for Neanderthals and Homo sapiens. And in the early 1900s, Cecil Whitney and his Acclimatisation Society pals created a hybrid zone in New Zealand when they introduced a bit of old England to the lakes and rivers of this country.
In line with typical colonial-era thinking of the day, the idea that the native grey duck might eventually be displaced by the incoming mallard was, to some, an inevitability—a continuation of the natural order of things.
Whitney himself said, “There can be no doubt, if let alone, the grey duck will very quickly be absorbed in the mallard. The true mallard is a better fighter, a stronger flyer, and a larger bird than the grey; and the grey will be much improved by mixing with the mallard… Eventually (when the grey has become absorbed, which will not be long), better birds will evolve from the two species.”
The ornithologist Walter Buller wrote that the grey duck was being “gradually supplanted by a superior bird in every way”.
By the 1930s, however, concerns about the future of the grey duck were being raised. Much of the discussion centred around the apparent reduction in the quality of the hybrid ducks as sporting birds. Mallard releases were brought to a halt. By now, though, the rampant pace of landscape change had accelerated and New Zealand was becoming a much more hospitable place for the introduced ducks.
“The wild wetlands were getting less wild,” says Williams. “There were fewer trees and a lot more people around. Mallards seemed to be much more comfortable in that sort of landscape.”
In the 1960s, the grey was still the most common duck on our waterways. By now, though, the mallard was in ascendancy. “They had a real advantage, in that they were more wary to the gun,” says Williams. “They had bigger clutches and raised more young. The grey duck was outbred, as well as being out-shot.”
That grey/mallard hybridisation was rampant was a given, but no one could say for sure how serious an issue it was. The problem was that the grey duck looked almost identical to the female mallard, so picking them apart in the field was next to impossible.
It wasn’t until the arrival of genetic analysis in the 1990s that the extent of hybridisation became clear.
“Most of the greys you see now will be of hybrid ancestry,” says Williams, “but you can’t easily tell. You’ll get two people looking at grey ducks and one will say, ‘That looks like a hybrid,’ and the other will say, ‘No, it’s a perfectly good grey.’ Neither of them will be totally clear about what to look for.”
The ducks in the Dunedin Botanic Garden that pad around my feet are no longer grey ducks or mallards—they’re an entirely new beast altogether. Some people have even given this duck a new name.
It’s called the “grallard”, and its presence in Aotearoa raises an ecological conundrum.
“They may be natural from a biological point of view,” Mead says, “but humans intervened by introducing these species without giving due consideration to the long-term impacts. We now have a situation where a species has been compromised to such an extent that it’s no longer its unique self.”
What is our kaitiaki responsibility towards hybrids? Do we protect them as the carriers of the whakapapa of older taonga species? Or see them as invaders?
The grallard is not alone. In the world we humans have made, more and more species are being brought into contact that might not have been otherwise and as a result, hybridisation is on the rise.
Black stilts (kakī) have been in New Zealand for around a million years, having originally flown here from Australia. They were once common throughout the South Island, but by the 1980s, after centuries of predation and habitat destruction, there were fewer than 30 left alive in the Mackenzie District. Today, they are the world’s rarest wading bird, their existence kept on life support by a captive breeding programme.
And now, kakī are not the only stilt on the waters of the South Island country.
The black stilt’s close Australian relative, the pied stilt, or poaka, arrived in New Zealand around 200 years ago, the same way the black stilt had—by being blown across the Tasman. Unlike the black stilt, the pied stilt was well used to mammalian predators, having evolved alongside them in Australia. It was also better suited to the open, deforested landscape created in New Zealand by humans.
And so, as kakī teetered on the brink of extinction, poaka flourished. Kakī and poaka readily interbreed, creating hybrid chicks that emerge somewhere on a colour spectrum from all black to fully pied.
Known as “smudgies”, these birds are seen as a threat to the genetic integrity of kakī and to this day, Department of Conservation (DOC) rangers closely monitor, and mediate, the breeding choices of black stilts.
Claudia Mischler is a DOC ranger, based in Twizel, whose job it is to enforce these rules.
“If it’s easy enough to find the nest of a mixed pair,” she tells me, “we will destroy the eggs, just so that those don’t hatch. We’ll put [the adult pair] on fake eggs, and leave them sitting on those to stop them from having more.
“If they’re in an area where there’s lots of black stilts and not many pieds, we will get rid of the pied stilts in the hopes that the black will pair up with another black.”
DOC uses a system of “nodes” to identify the degree of hybrid ancestry a bird has, based on the amount of black in their plumage. Birds in Node “J” (totally black) are prioritised for protection.
Mischler says there are areas of the Mackenzie District where hybrid stilts are common, but she and her team don’t take any direct action to reduce their numbers. The theory, backed up by one study, is that black/pied hybrids have less “reproductive fitness” (in other words, are less successful at breeding and hatching chicks) than purebreds, and therefore shouldn’t come to dominate, as long as pure kakī numbers can be maintained.
A recent genetic study led by Natalie Forsdick, a researcher with ManaakiWhenua/Landcare Research, found that despite decades of interbreeding, surprisingly little poaka genetic material has passed to the black stilts. This she largely puts down to successful management.
“Hybridisation is a really complex situation,” she tells me, “because there are potential benefits that you could get from it, in terms of new genetic material that could help improve species’ fitness.”
But if, as appears to be the case here, a species’ fitness is reduced, “you’ve got individuals that are basically wasting their reproductive potential producing birds that aren’t of their own species”.
The situation is complicated by the fact that New Zealand’s pied stilts are not “pure” either. In all likelihood, when they first arrived in New Zealand, they were heavily outnumbered by black stilts and so they bred with them. As a result, pied stilts in Mackenzie District all have a little bit of kakī in their genome.
Despite such head-spinning complications, Forsdick says it’s our responsibility to protect the rarer species from genetic pollution. “If humans hadn’t changed the landscape so much, there probably wouldn’t be an awful lot of habitat for poaka to get established in,” she says. “The chances of hybridisation would be slim. So we have the onus to maintain things.”
On Rēkohu/the Chatham Islands, the rare, yellow-crowned Forbes’ kākāriki, found only on Mangere Island and Little Mangere Island, interbreeds with the red-crowned kākāriki, which is a more recent arrival there. It is thought that historical forest clearance on the islands has brought the species together, and hence created the opportunity to hybridise.
For years, rangers visited the islands to remove hybrids, which they identified by their red crowns. However, Jamie Cooper, who currently leads the kākāriki programme on the Chathams, tells me hybrids have not been euthanised for around a decade.
“As the situation has changed on my island, there’s more forest, there’s more Forbes’ parakeets, and we’re actually finding that that problem isn’t as big as it used to be.”
DOC still keeps an eye on hybrid numbers, however. “Our hybrid classification goes in five steps,” says Cooper, “where number one is pure Forbes’ and five is pure red-crowned. We’re mainly focused on the hybrid levels of three, four, and five, which is orange in the crown. If we see over 10 per cent of the population of those, that would trigger a control measure.”
Hybridisation has also been detected in the world’s rarest kiwi, the rowi, which is found only near Ōkārito on the West Coast. A recent study, led by Lara Shepherd of Te Papa, found the species has in the past hybridised with little spotted kiwi, with which they once shared the bush. Not only that, but the syntype specimens (the collected specimens upon which the entire species is described) for the great spotted kiwi, held in the Canterbury Museum, were found to not be great spotted kiwi at all, but hybrids between little spotted kiwi and rowi.
Two little spotted/rowi hybrids have been shifted to the Marlborough Sounds to avoid further tainting of the rowi genome. No one, apparently, had the stomach to kill a kiwi, even a genetically impure one. Today, these two birds live together on Allports Island and have produced two chicks.
Dealing with hybridisation means drawing subjective lines and trying to live with some very difficult questions. If black stilts survive but end up with a few pied stilt genes in their genome, has conservation been achieved, or whakapapa preserved? Should we mourn the loss of the grey duck, or celebrate the creation of the “grallard”—a duck perfectly adapted to the human-modified environment it has emerged in?
“If we’re being good kaitiaki,” Mead says, “we’re keeping tabs on how all our relations are doing, and we’re keeping tabs on the integrity of their whakapapa. So, yes, there will be naturally occurring hybridisation. However, that should be the exception rather than the norm if we want to preserve the whakapapa of our indigenous species.
“It’s a balancing act. If there’s too much reproduction going on across species, then the balance is off.”
The grey duck is now listed by DOC as “nationally critical”, but no one can be sure any pure greys actually remain in New Zealand. According to a 2021 DOC report, it is possible, based on anecdotal reports, that a few thousand may persist in remote parts of Fiordland, the Canterbury high country, the Bay of Plenty and the Chatham Islands.
There is no management plan in place to protect grey ducks and, somewhat bizarrely, you can still shoot them—because they look so similar to mallards, there is no practical way to protect them from duck hunters without effectively banning all duck hunting.
DOC “considers the species at the lower end of priorities, given other species are classified as being at higher risk”, says the director of terrestrial science, Ian Angus.
And in any case, after a century of interbreeding, who’s to say where the mallard ends and the grey duck begins? What is actually left of the grey duck to protect?
What we have now in New Zealand, according to Murray Williams, is what’s known, with horror-movie overtones, as a “hybrid swarm” —a group of animals of mixed genetic heritage in which differentiation between one species and another is, without genetic analysis, no longer possible.
“At the end of the day,” he says, “if it looks like a grey duck and you think it’s a grey duck, you’re going to say it is a grey duck. But the old idea that you could have genetically pure grey ducks again in New Zealand… I think that ship has long left the harbour.”
So, should this concern us? It’s a philosophical, well, “grey” area that has absorbed much of Wellington ecologist Jamie Steer’s thinking. Steer is senior biodiversity adviser with the Greater Wellington Regional Council and has written extensively about hybridisation.
“From the perspective of the ducks themselves,” he asks, “what is the problem?
“The problem is our problem. We think it’s unfair to them that… these two strains have gotten mixed and that we were responsible for that, and we’ve got to make it right. But really, it’s only the geneticist who’s getting offended.”
In our highly altered system, he says, we have no choice but to accept a degree of fluidity.
“People think, ‘I’m happy with change, I just don’t want anything to go extinct,’” he says. “But that’s not how change works. It involves both the evolution of new forms, new ecosystems and new species and the loss of previous ones.
“I think we’re living in a bit of a fantasy land thinking that we can aspire to keep everything like it was in the past.”
That mallards would, at some stage, arrive in New Zealand was probably inevitable. They have found their way to many other parts of the world where, as in New Zealand, they have hybridised with local duck species.
Ducks are, in fact, serial hybridisers—a trait in part due to their mating behaviour. While the duck “couples” you see at your local park might appear to be cosy models of monogamy, extra-couple copulation (which, as Williams explains it, is a polite scientific way of saying “rape”) is common.
And just as black stilts may choose to mate with pied stilts, studies have shown that interspecific breeding between grey ducks and mallards is not a one-way affair. So, is it our place, Steer asks, to step in and try to control their choices?
“Are we continually going to mediate the sexual relationships of wildlife and say, ‘Well, you’re one species and you’re another and it’s just not right to mix like that? Even though you can produce fertile offspring that are perfectly healthy, you’ve got to understand that that’s wrong?’
“From a human perspective,” he says, “it’s kind of bizarre because it flies in the face of ways we treat human populations. We have quite distinct human populations which can interbreed, and of course, we’re quite happy with that.”
How mana whenua feel about hybrids varies from place to place and person to person. Aroha Mead points out that many Māori pūrākau, or legends, involve shapeshifting. Many taonga species hybridise naturally, and Māori traditionally assisted gene flow by shifting valuable ones, like pāua and shellfish, from one area to another.
“It’s all very fine to have a notion of a pristine environment and perfect species,” she says, “but if it’s not a problem for [mana whenua] then I guess it’s not a problem.
“It really depends on those who are the kaitiaki. And the impact that this might have with other species, whether it’s changing the whole ecosystem.”
I put the question to Murray Williams—does it actually matter if the grey duck in New Zealand isn’t what it used to be?
“Well, that’s going to be the bottom line of your article, isn’t it?” he laughs. “Do you like having ducks around you, whatever label you want to put on them? Or are you a genetic purist and want to get rid of mallards, which is completely impossible? Do you want to sit in a little box on the edge of a lake and hope something that looks like a grey duck flies by, so you can feel satisfied?
“It’s a value judgment, at the end of the day,” he says. “But this is the reality now: you’ve got two species that occupy a very similar way of life. They’ve integrated, and now the genes of the two are so intertwined that this is what you have.
“Get used to it.”