After three years of painstaking detective work and “Kiwi” ingenuity, it’s official: New Zealand has four species of kiwi, not three. The identification of the new brown kiwi, which has been given the name tokoeka, was announced by scientists in April after DNA cloning techniques similar to those popularised in the new sci-fi blockbuster Jurassic Park revealed profound differences between northern and southern brown kiwi populations. The tokoeka is the first new bird species to be identified in New Zealand since the takahe was rediscovered in 1948.
The researchers, Charles Daugherty from Victoria University and former Wellington Museum director Alan Baker, used two biochemical techniquespolymerase chain reaction (PCR) and allozyme electrophoresis—to analyse the genetic make-up of brown kiwis from around the country. Their findings confirmed what conservationists had suspected since 1979: that there are two distinct species of brown kiwi.
Surprisingly, the genetic break occurs at Okarito, half way down the South Island’s west coast, not between the two islands. The three populations of brown kiwi found south of Okarito (in Fiordland, Haast and Stewart Island) turn out to be genetically distinct from the Okarito and North Island brown kiwis.
Analysis of mitochondrial DNA (i.e. DNA that is not within the nucleus of the cell, but within the mitochondria) suggests that both species are derived from an ancestral Fiordland population. Baker suggests that birds from Fiordland spread north up the West Coast to Okarito, and then much later colonised the North Island at a time when there was a land bridge between the two islands.
At some point, speciation occurred—probably, say the researchers, during the ice age in the Pleistocene, when these flightless birds would have became isolated into small populations at high altitude. Isolation would have restricted their ability to swap genetic material, with the result that the populations would have diverged genetically, eventually forming distinct species.
As with all good detective stories, the hunt for the new brown kiwi involved some intrepid gathering of evidence, in this case by Department of Conservation officer Rogan Colbourne and his Labradors Tess and Lucy. Over a three-year period, Colbourne and his canine assistants trapped kiwis in the bush at Stewart Island, Haast, Fiordland, Okarito, Little Barrier and numerous North Island sites, taking blood samples from their legs.
“Tess and Lucy, suitably muzzled of course, would track down kiwis during the day while they were sleeping in their burrows. At night I would walk around imitating the kiwi’s calls, and catch the birds, using a net,” says Colbourne
“I had to take in my own laboratory supplies into the bush: centrifuges to separate the red blood cells, and liquid nitrogen to store the samples before sending them to Baker and Daugherty.”
Colbourne’s work for DOC has also helped identify physical differences between the brown kiwi species. For instance, South Island brown kiwis are larger than North Island birds. The Okarito population has a greyer plumage and white head markings around the eye and eyebrows, whereas the Haast birds which are of a reddish hue and the Fiordland population are brownish-grey.
The compact, squat North Island birds are distinct from the paler, more elongated southern ones. They are darker and have broader, scalier legs and long whiskers that reach to the end of their beaks. They have harsher, pricklier feathers, with small spiny ends, as compared to the softer, denser feathers of the South Island birds, and they have shorter necks.
Behaviour also varies between the kiwi species. In the North Island, the male and female share a single territory, and they eject their chicks from the territory after a year. Generally, the males, rather than the females, incubate the eggs, in clutches of two per year.
The Stewart Island birds live in groups of up to seven individuals, and appear to share nest duties. They have one egg per clutch, but sometimes have more than one clutch a year.
The Okarito kiwis are lowland birds, while the Haast birds live at higher altitudes—up to 1500 metres—and may move down for winter, or even hibernate—an aspect of kiwi research still uncharted. Okarito birds share the physical characteristics of the southern species but are genetically closer to the North Island species, leading scientists to suspect that the North Island populations are derived from the Okarito group.
Charles Daugherty began analysing kiwi blood in the late 1980s using allozyme electrophoresis, a technique he was also using to sort out tuatara species (see Issues 3 and 6). It is a simple enough process; you take a blood sample and pass an electric current through it. Because different proteins have different levels of mobility, you can map the proteins from each sample. Daugherty found that there were two basic types of brown kiwi, with a break occurring between them in the South Island. but felt that his findings were insufficient to make any firm claims.
It was at this point that Alan Baker’s research using PCR came in. The polymerase chain reaction enables scientists to copy sections of a gene (analogous to the “copy and paste” function in word processing programmes). The copies are then split off the original gene and sequenced to read the code. “The people producing Jurassic Park in Hollywood were interested in our work,” says Baker. “They called us up to check on the details.”
Baker compared the genetic codes for the Okarito and North Island populations and found they were very similar. “Every population showed a totally different code. No sequences were identical, but for these two populations the codes were very similar,” says Baker.
“Each molecule of mitochondrial DNA is mutating continuously. At the end of a million years there is a five per cent change in the molecule. That change takes place at a roughly constant rate, so if two kiwi populations are five per cent different genetically, they probably separated one million years ago. There are errors associated with this technique but it puts us closer to finding answers than before,” says Baker.
Baker’s genetic work matched Daugherty’s blood protein work very closely, and gave a finer resolution to the results.
Baker says further genetic research is now warranted, and predicts that the Haast, Fiordland/ Stewart Island, North Island and Okarito populations could prove to be separate species as well, giving a total of six kiwi species.
The news has been greeted with mixed feelings by DOC. “This discovery means we will have to change the emphasis of our work,” says Hugh Robertson, who runs the Department’s kiwi recovery programme. “We now have two threatened species of brown kiwi rather than one. So, in one sense this is a conservation negative, and makes our job harder.”
However, on the positive side, he says that DOC now knows it has to focus its limited resources on the key populations that need management, such as the 60-100 kiwis at Okarito. “This will help our captive breeding programme, so we can avoid mixing different species and populations,” he says.
Alan Baker is optimistic the discovery will open up new areas of research in New Zealand. “We are at the forefront of this ‘d-loop’ research. It is now quite likely that this technique will apply to other species.” Already in New Zealand it is beginning to be used to study native fish, the kiore (Polynesian rat) and the hoiho (yellow-eyed penguin). DOC is also funding Baker to do the same work on little blue penguins.
“Kakapo, kaka, keathey could all be studied using the PCR technique, and I would say that it is likely to detect some hidden or cryptic species. It also allows us to reconstruct the evolutionary history and biogeography of New Zealand’s biota.”
Daugherty, as well as using the allozyme technique on tuatara, has found that the common skink consists of four cryptic species—species which look the same but are genetically different—two of which are rare. He is now carrying out more research on skinks and geckos.
Who knows how many more subdivisions are to be found in New Zealand’s native species. Only time—and biological detective work—will tell.