It is easy to imagine how it could happen. A petrel, flying east from the Indian Ocean at the end of the Austral winter, makes landfall at New Zealand’s southern Codfish Island/Whenua Hou. Tired from its long journey, the petrel seeks refuge in the burrow of a green kākāpō: a critically endangered flightless species that is the world’s fattest parrot.
If the seabird intrudes when the kākāpō is primed to breed, the male parrot may attempt to mate with the smaller petrel, accidentally smothering it in the process.
In this case, there are two unwitting victims. The petrel harbours a deadly agent: H5 avian influenza. Soon after, bird flu begins to rip through the imperilled parrot population, pushing the waddling bird – which numbers fewer than 250 individuals – to extinction.
This is the kind of scenario that New Zealand’s conservationists are considering before the arrival of the spring migration season – as they have done for the past two years since a highly pathogenic strain of bird flu known as H5N1 began burning through global wildlife, spurring the largest sudden drop in the world’s bird population in decades.
Tens of millions of wild birds have succumbed to H5 worldwide, but so far Oceania has managed to keep the virus out – buying time for New Zealand to add another weapon to its arsenal before thousands of birds arrive from distant shores.
In August, the country’s Department of Conservation announced the completion of a world-first research trial showing that some of its rarest birds could be successfully and safely vaccinated against bird flu.
The effort is the latest in a global push to protect wildlife – not just farmed poultry – from the virus, which has also inflicted dramatic mass deaths among elephant seal, fur seal and seabird populations across the world. For those species already teetering on the brink of extinction, vaccination could be a gamechanger.
New Zealand is home to nearly 100 bird species found nowhere else in the world. Over the past year, the department has vaccinated up to 10 captive birds from five critically endangered species that have 500 or fewer individuals left – the kākāpō, takahē, kakī (black stilt), tūturuatu (shore plover) and one type of kākāriki.
The programme, using the H5N3 poultry vaccine, is the first to vaccinate so many species at the same time. After receiving two doses, a month apart, of the licensed poultry vaccine, scientists found that four species had built up a strong antibody response to the virus that lasted for at least six months.
“These species are dependent on captive breeding,” says Kate McInnes, a wildlife veterinarian and the department’s senior science adviser. Vaccination, she says, could protect core breeding populations in aviaries used for restocking wild populations on the knife-edge of survival, as well as managed kākāpō populations on offshore islands.
The next step is building a deployment strategy before spring migration, when travelling seabirds could introduce the virus. “You can’t just run around the forest and catch everything and jab it,” McInnes says. “You’ve got to have a really carefully planned programme in place.”
Other countries are watching the attempt closely. Australia is in close contact with officials in New Zealand about the vaccine results, and is running its own trials using stand-in species – animals similar to the critically endangered species but not endangered themselves – according to Fiona Fraser, Australia’s commissioner for threatened species.
“There is increasing concern now that the migratory bird season is just on our doorstep,” she says. Tens of millions of birds are expected to arrive in Australia in the coming weeks.
The Australian government last year announced it would allocate A$100m (£48m) to prepare for bird flu, including A$2.8m specifically to protect captive populations of threatened species.
“Having that extra time for our region to understand what the overseas impacts have been, and to get better prepared for Australian species, has been enormously important,” says Fraser. “We expect it’s not a matter of if, but when bird flu arrives in Australia. Because now that it is circulating in Antarctica, we are essentially surrounded.”
Vaccination, she says, makes up only a small part of the strategy. The country is focused on planning for species considered particularly vulnerable to avian influenza, such as the native Australian sea lion and Tasmanian devil, an endangered scavenger that could feed on the carcasses of infected birds.
Boosting the overall health of wild populations to help them withstand the eventual arrival of avian influenza is the priority, she says.
“Vaccinations can be stressful for wild animals and it cannot be as feasible as taking other measures such as improving their habitat,” Fraser says.
Australia’s policy on vaccination echoes the broader global view. Jabbing animals for conservation purposes is rare, although some programmes have been established to immunise koalas against chlamydia; vaccinate Ethiopian wolves against canine distemper; and develop a West Nile vaccine to protect endangered birds in Hawaii.
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The World Organisation for Animal Health noted in a 2023 committee report on the emergency vaccination of wild birds that it would be difficult to vaccinate wild populations against avian influenza with the currently available strategies.
“There are so many logistics that come into play,” says Krysten Schuler, a wildlife disease ecologist at Cornell University in New York state. Capturing and recapturing wild animals for multiple doses is difficult and expensive, especially for species that have short lifespans.
Nevertheless, when 21 California condors died from H5 avian influenza in 2023, the US government raced to intervene. About $20m (£15m) in federal and state funding has been spent on conserving the critically endangered vulture to date, making it one of the most costly US conservation projects in history.
Scientists first conducted trials of an H5N1 poultry vaccine on 20 black vultures and 20 captive condors. “We knew that this was going to have some international relevance – people were going to be watching it,” says Todd Katzner, a US Geological Survey wildlife biologist and research coordinator for the Condor Recovery Program. “It was the first controlled trial with a wild species.”
After finding that the vaccine yielded a successful antibody response with no harmful effects, the government approved an emergency vaccination campaign. By October 2024, they had inoculated 207 condors, including 134 “free-flying” birds.
An additional challenge, Katzner says, is that the trial vaccine used to jab the condors was based on a 2014 strain of avian influenza. “When they build human vaccines, there’s a huge economic driver to encourage them to stay up to date,” he says. “There is not a similar driver for bird flu vaccines, so you end up with vaccines that are out of date.”
Viruses evolve over time, meaning vaccines can be rendered less useful as the virus changes. Still, “the general sentiment was that a vaccinated bird will have better protection than an unvaccinated bird”, Katzner says.
Some scientists express reservations about jabbing wild animals. Viruses, they say, can quickly develop even more potent strains.
“A big concern with wildlife is incomplete vaccination that would actually lead to more viral evolution,” says Schuler. “Especially for a lot of these birds, they might be exposed to multiple avian influenza viruses. So by inserting a vaccination process in there, does it actually have the potential to sort out the ones that are more pathogenic – the ones that could be worse?”
New Zealand’s wildlife authorities plan to vaccinate its captive breeding populations of critically endangered bird species, as well as their offspring introduced to the wild, pending regulatory approval of emergency use of the vaccine. The timing of the programme depends on assessments of when the virus is likely to reach the country’s shores.
“If we start too soon, we’re going to lose that antibody because it will start to disappear,” McInnes says. “But if we start too late, we might have missed the crucial moment.”