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More than 150 of Australia’s native and unique bird species have been assessed as being at “very high risk” of extinction or major decline if they catch the deadly H5N1 bird flu strain, with Western Australia’s celebrated black swans among the most susceptible.

The federal government analysis of Australia’s 800 different birds and 350 mammals reflects the high level of concern among experts about the arrival of the H5N1 strain, which has killed millions of birds and mammals around the world.

Australia was the only continent free of the contagious strain until tests confirmed a brown skua and a giant petrel – found sick a few kilometres from each other on the Western Australian coastline near Esperance – both had the strain.

On Tuesday, WA authorities said no new cases had been found and there was no evidence the virus had spread into other wild populations.

State and federal governments have been preparing for the likely arrival of the disease for several years, including the development of 100 response plans for species and habitats and a risk analysis for Australian species.

A federal environment department spokesperson said: “Many of our birds and mammals are not found anywhere else in the world, making the impacts of H5 bird flu difficult to predict.”

There were more than 150 bird species unique to Australia “considered at very high risk” under the risk analysis, the spokesperson said.

They included the red goshawk, fairy tern, plains-wanderer, shy albatross, black swan and western hooded plover.

Migratory species like the short-tailed shearwater – famed for its 15,000km migration from the Arctic Circle to Australia – were also at very high risk.

At a high risk were the swift parrot and orange-bellied parrot, both critically endangered in Australia.

Chris Purnell, the wetland and migratory shorebird program manager at BirdLife Australia, advised on the analysis and said it had considered both the risk of extinction at a species level or at a regional population level.

“For these endemic birds, there’s no avenue for repopulation from outside Australia. If they are gone, then they are gone.”

More than 10 mammal species, including the already endangered Australian sea-lion as well as the subantarctic fur seal and the Australian fur seal, were also assessed as very high risk.

Other species which “may be at high risk of H5 bird flu” included the Tasmanian devil and eastern quoll, the spokesperson said.

The WA agriculture minister, Jackie Jarvis, said further testing of birds reported as sick or dead by members of the public had detected no new cases so far.

Western Australia’s famous black swans are considered highly vulnerable because they lack some of the immune genes that have helped other waterbirds combat the virus.

A team of scientists published research in 2023 that sequenced the genome of the state’s bird emblem and compared its immune response with white swans.

Black swans lacked the necessary components to detect H5N1 and had a heightened inflammatory response when cells were infected.

“What it means is it has the wrong type of immune response to the virus,” said Prof Kirsty Short from the University of Queensland and a lead author of the research.

“Instead of detecting the virus and having a very controlled inflammatory response, it doesn’t detect the virus and has an out-of-control, pro-inflammatory response.”

She said if the disease took hold in local wildlife populations, “we could see widespread mortalities” of the species.

“They have been proposed as a sentinel species, meaning if we do see widespread mortality of black swans it’s a good indicator that there’s a lot of H5N1 incursion because they’re so susceptible,” she said.

Short said “the big picture is really that our native species might be particularly at risk of severe H5N1”.

“We don’t know because most of the studies have been done in northern hemisphere animals and not in our unique species. This is why we did the black swan, to do something Australian-specific.”

Purnell said because black swans had many breeding populations around Australia, bird flu was “unlikely to be an extinction threat for black swans but it could have high impact and high mortality in specific localised regions”.

“The highest mortalities are going to be in species that congregate together in dense groups, such as pelicans,” he said.