A dolphin has died from H5 bird flu in South Australia, marking the second native mammal species known to have contracted the virus.

On Friday afternoon, the Tasmanian government said it was assessing the discovery of about 100 dead little penguins on King Island but it was unable to test them for H5 bird flu due to their “decayed condition”.

It comes as the federal government announced it would withdraw researchers from the sub-Antarctic Macquarie Island research station due to the “psychosocial risk” of witnessing potential mass seal deaths from H5N1 during the upcoming seal breeding season.

The common dolphin was found recently deceased near Goolwa on South Australia’s Fleurieu Peninsula. State tests confirmed the animal was positive for H5N1, with samples sent to the Australian Centre for Disease Preparedness for further analysis.

It follows two earlier detections in long-nosed fur seals in SA at Beachport and the Pages Islands and a case in a red fox – a feral pest species – near Port Adelaide.

The federal government’s risk assessment rated common dolphins at high risk from bird flu, meaning they potentially face severe population declines where the virus takes hold.

“While the detection in the common dolphin is a new development in Australia, there is evidence of dolphins and porpoises catching H5 bird flu overseas,” a spokesperson for SA’s Department of Primary Industries and Regions said.

“Dolphins would not commonly eat birds but it is not unusual for them to sometimes interact.”

In Tasmania, the state government said about 100 dead little penguins were found at Stokes Point, the southern tip of King Island, during wildlife monitoring activities. The government has labelled the deaths a mass mortality event but said the cause had not been established.

The natural resources and environment department said the birds were not considered suitable for H5 bird flu testing due to their decayed condition.

Brendon Clark, north-west regional manager for the state’s parks and wildlife service, said authorities were working to “assess the circumstances surrounding the discovery and determine whether any further management actions are required”.

“Any loss of wildlife is concerning, and we recognise this discovery will be upsetting for residents, visitors and others who care deeply about Tasmania’s unique wildlife.

“While assessments of the site have identified injuries on many of the birds, it is not possible to definitively determine the cause of death from the information currently available.”

He said monitoring of the site would continue.

The federal government said on Friday it would withdraw 24 expeditioners based at the research station on Macquarie Island in the Southern Ocean about 1,500km south-east of Tasmania.

While bird flu had not yet been detected on the island, it was home to large elephant seal populations close to station buildings. Expert assessments had predicted “a high likelihood of a significant mortality event during the upcoming breeding season”.

“While the risk to humans remains low, a significant mortality event during the upcoming seal breeding season could expose expeditioners to prolonged psychological stress and other workplace impacts,” the department said.

The department’s deputy secretary, Sean Sullivan, said: “This is an unusual measure, but is the most appropriate course of action, based on our assessments of risk, and operational realities.

“Our first priority is the health and safety of our expeditioners. While the risk to humans of H5 bird flu is considered low, we can’t ignore the psychosocial risks of living near potentially large numbers of affected animals.”

Sullivan said the researchers lived and worked in one of the world’s most remote and challenging environments.

“We’ve seen what this disease can do, based on our experience at Heard Island and McDonald Islands.”

Drone surveys detected more than 13,000 dead southern elephant seal pups on Australia’s Heard Island in 2025 and 2026.

Sullivan said the decision had been made to minimise the risks to researchers and “across the whole Antarctic program” in advance of any mass mortality event.

He said Macquarie Island was unique in that thousands of elephant seal pups were born close to the station every spring.

“No other Australian Antarctic station is in this position, and there are no elephant seal colonies on mainland Australia,” he said.

Sullivan said the government was exploring options for monitoring the situation on Macquarie Island, with a view to “returning expeditioners to the station in coming seasons”.

The SA government said on Friday it would move to confirming H5 bird flu cases in the state through local laboratories. Until now, state-based test results have required verification by the CSIRO’s Australian Centre for Disease Preparedness in Geelong. The state government said improvements to its testing processes meant confirmation of H5N1 cases could now be done locally.

The New South Wales government also announced its plans to vaccinate wild populations of little penguins at Manly and Barunguba Montague Island.

The government also said “trial cohorts” of some captive bird populations, including little penguins, Carnaby’s black cockatoos and red-tailed black cockatoos, had received the first vaccinations at Taronga zoo this week.