New DNA insights have just changed what we thought we knew about another famous New Zealand bird - our feisty, flightless weka.

The number of sub-species of weka has been a point of debate, with the land bird being found on mainland New Zealand and many islands, including Stewart Island and the Chatham Islands.

Previously, weka were thought to comprise up to six sub-species, but new data just published by Massey University biologists suggests just two: Gallirallus australis greyi in North Island and Gallirallus australis australis in the south.

The researchers say these sub-species were classified based on anecdotal colour differences in feathers, rather than significant differentiation.

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Lead author and evolutionary biologist Professor Steve Trewick said the sub-species finding was trumped by what they found out next.

"The naming of species is something that we humans do to classify our world, but as evolutionary biologists we are looking to delve further," he said.

"When we are talking about bird populations in New Zealand, there is a lot of interest in the difference between populations which live in the North and South Islands and how those gaps affect them.

"When you are talking about flightless birds, even the 25km Cook Strait is seemingly evidence enough to conclude why two sub-species stayed separate and never mixed.

"However, we now have evidence that when the north and south were connected by land, the two subspecies still didn't mix enough to join the two populations."

The work tied into studies around the world seeking to understand how geography and biology interact in the formation of regional biotas.

The findings were made possible by looking at not only the DNA of weka, but also of their feather lice, as each weka sub-species was found to have its own distinct lineage of feather lice.

"While it may seem odd to study a bird's parasites to understand more about their host, they are actually remarkably handy as the lice end up sharing their evolutionary history with the host," Trewick said.

"If individuals resulted from breeding between northern and southern weka, they could have northern and southern weka lice, which they do not."

The findings were part of a much larger effort to understand the pattern of North Island and South Island races in many New Zealand birds.

Data from other species were examined also, including Karearea falcon, Toutouwai robins and Kereru pigeon.

Weka populations are subject to large fluctuations, with numbers increasing during favourable conditions and declining abruptly when food becomes scarce. Photo / File
Weka populations are subject to large fluctuations, with numbers increasing during favourable conditions and declining abruptly when food becomes scarce. Photo / File

"The more we understand about their past and how it affects their genetics, the more we can tell about the remaining populations."

Weka populations are subject to large fluctuations, with numbers increasing during favourable conditions and declining abruptly when food becomes scarce.

Moist islands and those with rich soils supported the most stable populations.

Because of its scavenging habit, the weka has proven problematic for conservationists - in some cases, moving them to offshore islands could disrupt other threatened wildlife species, especially lizards, seabirds and other ground-nesting birds.

The decline and destabilisation of weka populations on mainland New Zealand, which has resulted in legal protection, has also inhibited mahinga kai in modern times.

Some iwi today welcome conservation projects that would potentially enable the restoration of harvesting while others believe that the time for harvest has gone.

The only place where the legal harvest of weka can occur is on the Chatham Islands and on some islands around Stewart Island.

Creatures redefined: 10 DNA discoveries

The karearea (New Zealand falcon). Photo / File
The karearea (New Zealand falcon). Photo / File

KAREAREA:

Last year, Trewick and colleagues drew on DNA to show New Zealand's native falcon isn't one species but two sub-species that live separately on the North Island and South Island. Their study, examining the body sizes and genetic makeup of the karearea, found strong evidence for two distinct sizes within the species, with the North Island form being smaller than the South Island one.

The Stewart Island shag. Photo / Gary L Clark
The Stewart Island shag. Photo / Gary L Clark

STEWART ISLAND SHAG:

DNA technology solved a quirky case of spot-the-difference and revealed New Zealand's "newest" two seabirds. Until an Otago University study last year, the newly-described Foveaux shag and Otago shag had been grouped together under the single name of Stewart Island shag.

Remains of the Kohatu shag's skull. Photo / Jean-Claude Stahl, Te Papa
Remains of the Kohatu shag's skull. Photo / Jean-Claude Stahl, Te Papa

KOHATU SHAG:

Bones strewn through fossil deposits in Northland and museum collections were this year found to belong to a previously undescribed, extinct species of shag. It had been thought that the bones were those of the King Shag, which lives at the top of the South Island. But by examining the shape of the bones and using modern and ancient DNA, a team of New Zealand researchers found that there was actually an entirely different species of shag - dubbed the Kohatu shag - which is now extinct.

The plump and peculiar-looking Chatham Island parrot had a beak described as halfway between that of a kaka and a kea. Photo / Landcare Research
The plump and peculiar-looking Chatham Island parrot had a beak described as halfway between that of a kaka and a kea. Photo / Landcare Research

CHATHAM ISLANDS PARROT:

Ancient DNA was used by Landcare Research scientists to reveal, in 2014, a new species of endemic parrot. Unfortunately, birdwatchers are unlikely to have much luck if they go looking for the Chatham Islands parrot, as it has already been extinct for several hundred years. The plump and peculiar-looking parrot had a beak described as halfway between that of a kaka and a kea.

NZ sea lions on subantarctic Enderby Island. Photo / File
NZ sea lions on subantarctic Enderby Island. Photo / File

NZ SEA LION:

In 2014, Otago scientists discovered a pre-historic mainland species of sea lion thought to have been wiped out by Polynesian settlers and replaced by the modern New Zealand sea lion. The researchers concluded that the pre-historic species, which once dominated South Island shores, became extinct as recently as 600 years ago before a lineage previously limited to the waters of the cold subantarctic took their place.

Kiwi are more closely related to Madagascar's elephant bird, rather than any Australian ratite species. Photo / File
Kiwi are more closely related to Madagascar's elephant bird, rather than any Australian ratite species. Photo / File

KIWI:

2014 was also the year that scientists corrected the shocking suggestion that our national bird arrived here when its winged ancestor flew in from Australia. The 150-year-old mystery was finally solved by DNA sequencing that revealed the bird was more closely related to the extinct, 2.3m tall elephant bird, a native of Madagascar.

The extinct moa, which once existed in huge numbers. Photo / File
The extinct moa, which once existed in huge numbers. Photo / File

MOA:

Another 2014 study put even more genetic distance between the extinct moa and their old bush mates, the kiwi. This suggested the giant birds were more closely related to a flying South American bird still alive today than our national icon. The South American tinamous, one of the world's most ancient living groups of bird, can fly and are not categorised as ratites, but are considered close relatives because of the shared structure of their palate bones.

A yellow-eyed penguin in Oamaru. Photo / File
A yellow-eyed penguin in Oamaru. Photo / File

YELLOW-EYED PENGUIN:

DNA analysis and carbon-dating led to findings that revealed a change-over between the yellow-eyed penguin and another penguin species that became extinct around the same time as the moa. An Otago team showed the waitaha, which was slightly smaller than the yellow-eyed penguin, vanished within 200 years of Polynesian settlement of New Zealand, before 1500AD. In one of the most rapid biological transition events documented, the yellow-eyed penguin, or hoiho - considered one of the world's rarest penguin species with a population of between 6000 and 7000 - moved to the mainland from the subantarctic islands and replaced the waitaha within just a few decades, in the early 1500s.

A little blue penguin in Wellington. Photo / File
A little blue penguin in Wellington. Photo / File

LITTLE BLUE PENGUINS:

In December, Otago researchers described not one but two distinct species of little blue penguin in New Zealand - and two months later revealed how an Otago sub-population had travelled across from Australia at some point between 1500 and 1900.

A complete mounted skeleton of the extinct Pouwa. Photo / Museum of New Zealand Te Papa Tongarewa
A complete mounted skeleton of the extinct Pouwa. Photo / Museum of New Zealand Te Papa Tongarewa

POUWA:

In July, researchers revealed how New Zealand once had its own species of black swan but, like the moa, it was hunted to extinction soon after humans arrived in the late 13th century. Pouwa were much heavier and larger than their Australian cousins, which are now common around New Zealand, and were on the way to becoming flightless when they became extinct.