One of New Zealand's rarest native birds has shown how threatened species everywhere are facing a tougher time adapting to our fast-changing planet.

Scientists have already shown how domesticated animals and wild creatures that aren't threatened can adapt to different environments if they're flexible enough, could shift ranges, or can simply evolve.

But new research has painted a more troubling picture for those species moving toward the brink.

Because threatened species typically couldn't move – either because most of their habitats had been destroyed or because the risk of shifting was too dangerous – the researchers wanted to know whether they could adapt genetically.

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That prompted them to look for the genetic variation necessary for this to happen – or the influence that genetics, through inheritance, might have on characteristics that were important for survival and reproduction.

"This is important because if a species or population have low levels of genetic diversity, they will find it much more difficult to cope and survive changes in their environment - be it changes in climate, or new diseases, or other challenges," said the study's co-lead author, Dr Anna Santure, of the University of Auckland.

The team found the hihi, or stitchbird, a perfect candidate to answer their questions.
This owed to more than 20 years of demographic and genetic data that had been collected at the hihi's Hauraki Gulf island stronghold of Tiritiri Matangi, where the bird had been translocated from their remnant population on Little Barrier Island.

Added to that, the research team knew their island habitat had always been closed off – and that they could draw upon plenty of studies about the hihi's history, behaviour, ecology and physiology.

"Hihi have been closely managed since the early 1990s and the recovery programme has become a globally important example of successful recovery of small populations," said study co-author Dr John Ewen, a senior research fellow with the Zoological Society of London.

On Little Barrier Island, hihi were now estimated to number between 600 and 6000 adults.

"Science is clearly embedded in management and our monitoring provides the evidence required to identify and overcome management challenge," said Ewen, who also serves as co-chair of the Hihi Recovery Group.

"This approach has been highly successful and we now can celebrate having hihi spread across six reintroduced populations in northern New Zealand, in addition to the remnant population."

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In the new study, supported by a Marsden Fund grant, the wealth of data was combined with the latest technology to infer the genetic contributions to traits that would help populations survive and thrive.

"The long-term study of hihi is a globally very significant dataset, as there are very few datasets of this quality for threatened species," Santure said.

"One thing that makes the Tiritiri Matangi dataset very special is that data is available for every individual in the population from birth to death, so that we can get very accurate estimates for fitness and selection."

Next, they were able to generate genome-wide data to measure the amount of genetic diversity among 31 birds from Little Barrier Island and Tiritiri Matangi.

By linking all the results, they found there was little genetic contribution to the traits that mattered – and this correlated to a lack of genetic diversity found in the species.

New Zealand's threatened hihi now numbers only in the thousands. Photo / John Sibley
New Zealand's threatened hihi now numbers only in the thousands. Photo / John Sibley

In fact, they revealed the genetic diversity in hihi was five times lower than in any unthreatened species they could compare it with.

"Our management choices often focus on genetic factors and this will raise questions on our ability to preserve adaptive potential, and how we best support recovery of rare species, given this challenge," said the study's co-lead author Dr Patricia Brekke, also of Zoological Society of London's Institute of Zoology.

"One thing is for sure, we can recover these species and this type of knowledge will help us do so more efficiently.

"Genetics is just one of many challenges species like hihi face and as conservationists we figure out solutions to them - so our findings need to be placed alongside all threats rather than siloed."

It's not the first time hihi have illustrated the crucial need for genetic diversity in conservation management everywhere.

Last year, the University of Otago's Dr Helen Taylor organised what was one of the oddest conservation campaigns ever mounted – The Great Hihi Sperm Race – to raise funds and awareness.

The new study, just published in the scientific journal Current Biology, was also co-authored by Dr Pierre de Villemereuil, from the Centre for Functional and Evolutionary Ecology in Montpellier, France, Dr Alexis Rutschmann and Kate Lee, from the University of Auckland's School of Biological Sciences.