Kiwi are flightless, nocturnal birds that are native to New Zealand. There are five recognised species of kiwi, and with 400 remaining individuals, the rarest is the critically endangered Rowi (Apteryx rowi) of New Zealand's Okarito forest. The second rarest species is the little spotted kiwi (Apteryx owenii), which has been spread over several of New Zealand's smaller islands since becoming extinct on the mainland more than 30 years ago. The species' steady increase from just five individuals to around 1,600 is considered so impressive, they're the only species of kiwi not currently classified as threatened, despite how rare they are. But a new study investigating their genetic diversity has revealed that the little spotted kiwi may be in more danger than we thought.
With a length of 35 to 45 cm in males, and weighing little more than a kilogram, the little spotted kiwi is the smallest species of kiwi. It owes the second half of its name to its shaggy, mottled grey and white feathers. While their wings are negligible, they are fast runners, and they use their powerful legs and claws to defend themselves. Adults typically form monogamous pairs that can last for decades, during which time they'll usually produce one or two chicks per year. Very little is known about the species, including at what age they become sexually mature, but it's thought that they can live to be 100 years old.
The little spotted kiwi was once widespread on the North and South Islands that make up the mainland of New Zealand, but introduced predators such as cats, dogs and stoats, a reduced habitat and an enormous skin trade saw them decline rapidly in numbers, disappearing altogether from the North Island by 1900. During the 1980s, the little spotted kiwi was declared extinct on the South Island too. Fortunately, two populations existed on the nearby D’Urville and Kapiti Islands. D’Urville and Kapiti sit about 75 km apart on opposite sides of Cook Strait, which separates the North and South Islands, and D’Urville is about 500 m from the South Island while Kapiti sits 5 km from the North Island.
Historical records suggest that in October 1912, five little spotted kiwis were introduced to Kapiti Island from the South Island's Jackson Bay as part of a conservation management program. No other little spotted kiwi have been moved to Kapiti since, but they managed to breed themselves out of a severe genetic bottleneck situation, which describes a sharp reduction in population size, into the species' biggest population, with around 1,200 individuals today.
While the original D'Urville population went extinct by the early 1980s, the last-known female and male were moved to the predator-free sanctuary of Long Island, which is part a series of drowned valleys poking up out of the Pacific Ocean near New Zealand's South Island, known as the Marlborough Sounds. Two males from Kapiti were also moved to Long Island, and a Kapiti female joined them in 1989. The Long island population now stands at about 50 individuals. Around the same time, groups of 12 to 40 little spotted kiwi were transported from Kapiti Island to six other predator-free island sanctuaries around New Zealand in an effort to safeguard the species. All populations have been experiencing positive population growth to this day.
Because the Long Island little spotted kiwi population was founded by individuals from both Kapiti Island and D'Urville Island, it was hoped that it harboured the most genetic diversity, and hence the most value for the future of the species. A team led by Kristina Ramstad, a geneticist from the Allan Wilson Centre for Molecular Ecology and Evolution at New Zealand's Victoria University of Wellington, and Rogan Colbourne and Hugh Robertson from the Department of Conservation at New Zealand's Research and Development Group, ran a genetic survey on little spotted kiwi from four populations on the Kapiti, Long, Tiritiri Matangi and Red Mercury Islands. "There were all these ideas floating around about what the genetic diversity of the little spotted kiwi would look like, but it had never been measured at all," says Ramstad. "In the meantime, there was this concern that they probably have low diversity, and we need to find the D'Urville Island offspring and move them."
But what they found through a genetic analysis several little spotted kiwi populations, was that the D'Urville Island male and female that were put on Long Island in the 1980s - the birds upon which all hopes of substantial genetic diversity rested - had never actually bred. They didn't even produce one chick. Which means that all the little spotted kiwi on the planet, from every population, have come from the five birds that were originally put on Kapiti Island in 1912. And even worse for the Long Island population, the analysis revealed that nearly all of them were the direct offspring of a single mating pair.
The team found that the oldest known little spotted kiwi on Long Island, a 34-year-old male, was one of the founding three moved from Kapiti Island to Long Island in the 1980s. Because the D'Urville birds didn't breed, this old Kapiti male and his mate are essentially the kiwi version of Adam and Eve. Ramstad estimates that around a fifth of the entire population are his second generation offspring, or grandchildren, and the rest would be his sons and daughters. It doesn't get more inbred than that, and instead of being what was assumed to be the most genetically diverse population, with a combination of Kapiti and D'Urville birds, Long Island actually harbours the least genetically diverse population. "We don't know why [the D'Urville birds didn't breed]," says Ramstad. "We don't know how long little spotted kiwi live and we don't know what's their oldest age of reproduction. It's still a bit of a guess, they keep outliving the scientists following them. So the birds [from D'Urville Island], could have been too old, or one of them could have been infertile. It could simply be a case that they didn't fancy each other."
Ramstad was also shocked by how quickly the little spotted kiwi populations were losing genetic diversity. In the largest population of 1,200 birds on Kapiti Island, the analysis revealed that they were behaving genetically like a population of just 40 birds. Each of the populations were found to be losing genetic diversity with every generation, and were all going through the process of genetic erosion in different ways, which is a danger to their evolutionary longevity. "I think these findings were a surprise to everyone. In fact, I know they were, even the people who thought there'd be low diversity," says Ramstad. "We were also shocked to find that a population as big as Kapiti looks like it didn't just came from five birds, but all of the genetic diversity in that population could be explained by just three of those birds reproducing, two of them being female."
New Zealand's Department of Conservation is now reviewing the analysis, which was published in Proceedings of the Royal Society B today, to figure out how to ensure the future of their iconic and beloved bird. Ramstad believes that the results will likely see a change in the classification of the species to threatened or endangered. "What this study has told us is we need to be more careful. But the Department of Conservation are doing the right thing, and that is, don't keep all your kiwi on one island, [because] what if one island is reinvaded by stoats, what if someone sets fire to one island? They've got the kiwis spread over multiple islands, and they are now going to be gauging if they need to take more birds from Kapiti Island and to those smaller, more recently founded populations that are now experiencing a second bottleneck to boost their genetic diversity."
A new study is now underway to figure out how the inbreeding in little spotted kiwis is affecting their health, and Ramstad is conducting a similar genetic analysis on the critically endangered Rowi, a species that has also gone through a genetic bottleneck situation of just 180 individuals before growing to a population of around 400 today. "It's such a privilege to be able to work with these birds. To be in a position where my research could tell anybody something new about kiwi is always exciting. It's meant a lot to me to work on them and understand them on this level."