The arrival of the highly pathogenic H5N1 strain of bird flu in Aotearoa New Zealand last month triggered a national response years in the making.
By then, surveillance systems, species protection plans and even vaccines for some birds were already in place as part of a coordinated approach led by the Ministry for Primary Industries.
Yet even these preparations may not be enough to save some of the country’s rarest birds. Many survive in tiny, isolated populations with limited genetic diversity.
For these highly vulnerable species, the outcome may depend not only on conservation efforts, but also on chance.
Genetic diversity acts as nature’s insurance policy against disease. In large populations, some individuals are more likely to survive an outbreak and help the population recover.
But in small, isolated populations with little genetic diversity, those odds are much lower, leaving species far more vulnerable to extinction.
Why vaccines can only do so much
H5N1 has caused mass mortality events in wild birds around the world since emerging in 2020, making it one of the most significant disease threats many species have faced in decades.
Vaccines offer one important layer of protection, but they are no silver bullet. A Department of Conservation-led vaccine trial involving five intensively managed threatened species found that effective protection requires at least two doses administered a few weeks apart.
In kakī – the critically endangered black stilt and one of the world’s rarest wading birds – immunity declined after three months, meaning a third dose will be needed.
With the trial now complete and H5N1 in New Zealand, vaccinations are underway, beginning with 300 individuals from the five species involved in the study.
The greater challenge, however, is delivering that protection in the wild. Catching a threatened bird once can be difficult. Catching the same bird again, at exactly the right time for a second or third dose, can be harder still.
Vaccinate too early and immunity may wane before the virus arrives. Vaccinate too late and the opportunity may be missed.
These practical constraints mean conservation teams cannot simply vaccinate every bird. Instead, they must make difficult decisions about where limited time and resources will have the greatest impact.
On Rēkohu/Wharekauri/Chatham Islands, for example, plans are underway to vaccinate several of its threatened species, including black robin (karure, kakaruia).
The species’ small population on Maung’ Rē/Mangere may make it possible to vaccinate every individual with two doses.
On nearby Hokoreoreoro/Rangatira, however, the larger population is likely to require a different approach, with efforts focused on vaccinating as many birds as can be reliably caught and recaptured while balancing the needs of other species.
The harsh reality is that some birds will receive the right protection at the right time, but others will not.
Different birds, different risks
Just as importantly, not all species face the same level of risk from H5N1. It varies depending on where those species live and how they behave.
For colonial nesting species such as many seabirds, breeding creates the ideal conditions for the virus to spread, as birds gather closely in large numbers.
For solitary nesters such as kakī, however, breeding is one of the safer times of year because individuals are more widely dispersed. Their risk increases outside the breeding season, when they congregate at estuaries alongside other bird species.
If bird flu does push some species even closer to extinction, it will not be for lack of effort. Across the country, dedicated teams will be working tirelessly to protect the country’s most vulnerable wildlife.
To date, the incursion remains limited. Two wild birds in the Wellington region have tested positive for H5N1, with no further detections since mid-July and no evidence of widespread mortality in wildlife or spread into poultry.
But overseas experience has shown how quickly the situation can change, making continued surveillance and preparedness essential.
Recent media coverage of an injured ruru (morepork) offered a glimpse of how difficult and emotional those decisions can be. In the months and years ahead, conservation staff will need not only the best available science, but also patience, understanding and kindness from the communities they serve.
For now, H5N1 is the immediate threat. It is unlikely to be the last.
As emerging diseases become an increasingly important conservation challenge, building resilient species and ecosystems will be just as important as responding to each new outbreak.
If you find a single sick, injured or dead native bird, contact the Department of Conservation (0800 362 468). If you find three or more sick or dead birds together, report it immediately to the Ministry for Primary Industries (0800 80 99 66).
This article was originally published on The Conversation. Read the original article.
