Helicopter surveillance has revealed 49 dead greater crested terns on Baudin Rocks, near Robe, with 35 more sick terns, authorities reported on Saturday. Some of the birds have been collected for testing, and South Australia's chief vet, Skye Freuan, said it was likely the first mass mortality event from the H5N1 virus.
Spread inland and to other species
South Australia also reported three suspected positive cases in other greater crested terns, including one inland at Monarto, an area home to several poultry farms. Three silver gulls are also suspected positive, SA authorities said, adding to a first silver gull that was confirmed positive by the CSIRO earlier on Saturday.
Kate Millar, chief executive of BirdLife Australia, called the development a "very significant escalation of the bird flu situation in Australia, and a very bleak milestone."
"Sadly, we're at the beginning of a long and challenging battle and birds and wildlife are going to need all the help they can get," she said.
Jack Gough, chief executive of the Invasive Species Council, said the disease now appeared to be "starting to take off" and "mirroring the experience in South America of early detections, then rapid increases in numbers and spread leading to mass mortality events in wildlife."
"We are still at the very early stages of this devastating disease spreading, but the possible first mass mortality coming just days after the virus was declared not eradicable indicates how quickly this could escalate," he said.
Freuan said there was "nothing we can do" to stop the spread of the disease, but that surveillance was working.
Rapid escalation in a week
The detection came at the end of a significant week for the disease in Australia, with reported numbers jumping by 20 in just a few days to a current total of 53. Australia was the last continent to record the arrival of the virus, which has killed millions of birds and mammals worldwide.
Victoria this week confirmed its first cases of the virulent strain in a greater crested tern found in Portland, joining Western Australia, South Australia, New South Wales and Queensland in recording positive cases. On Saturday, Victorian authorities said samples from five crested terns had been sent to the CSIRO laboratory in Geelong, with preliminary testing suggesting more positive results.
Five confirmed cases in birds at Seal Bay on Kangaroo Island have also raised concerns for the area's Australian sea lions, an endangered species, with tens of thousands of seals having died worldwide from the disease.
Silver gulls could carry the virus inland
It is the cases among silver gulls that have experts concerned the spread has reached a critical new stage. Sean Dooley, national affairs adviser at BirdLife Australia, said silver gulls are very common and mostly coastal but can also come inland.
"When people think of a seagull, they're almost always thinking of the silver gull," he said.
"They're very common, and primarily they are coastal, but they do come inland and can turn up in Lake Eyre following floods," Dooley said.
Silver gulls are the second Australian native species to catch the disease, after dozens of detections in greater crested terns. Their scavenging habits mean they can easily pick up the disease from dead or dying animals, and they also pick up detritus from lakes and flooded areas, which are known breeding grounds for the virus.
"There is such a large population of silver gulls, and they move into other habitats. They could be the vector that takes bird flu inland," Dooley said. "They're also really successful in urban areas and could bring the disease into those bird populations."
Because Australia has a high concentration of unique birds, the susceptibility of many native species is unknown, but there is no reason to think they would fare better than birds overseas. Species that flock around water have tended to be the hardest hit, including sandwich terns, black-headed gulls and northern gannets in Europe, and pelicans in Peru.
Dooley said the mood at BirdLife Australia this week had been one of "trying to suppress that sinking, gut-churning feeling." The winter season for birdwatchers along the coast had been one of the best in 10 years, with rare petrels appearing in numbers along the east coast.
"Now that has been heavily tinged because probably among those were birds carrying H5N1," he said.
