Antarctica has never had an outbreak of highly pathogenic bird flu before and its residents are likely to have few immune defenses against the virus. “The populations are completely naïve,” said Dr. Thijs Kuiken, a veterinary pathologist at Erasmus University Medical Center in the Netherlands and an author of the new report. “The worry is that the first time that it goes through, it will really have a high impact in terms of rate of mortality.”

Many of the region’s birds, including emperor penguins and sooty shearwaters, are already facing other threats, from sources including climate change, the fishing industry or other human activities. Some species, like the southern pintail and the Macquarie shag, are restricted to just a few islands. “So if you were to get an outbreak in those islands, basically the whole species collapses,” Dr. Vanstreels said.

Local marine mammals could be at risk, too. Although the Antarctic fur seal can range widely, 95 percent of the population lives around just one island, making it vulnerable to an outbreak.

At this point, the virus is so widespread that it may not be possible to stop it from reaching Antarctica. “At the moment, there’s nothing we can do to prevent it,” Dr. Kuiken said. “So it’s important in the coming months to be as alert as possible.”

It will be critical to monitor wild populations to learn more about how the virus is spreading, what species might be most at risk and what conservation actions might be needed to help them recover, scientists said. “What we’re trying to do is document this really well, trying to understand how the virus is moving to see how we can better protect the species going forward,” Dr. Uhart said.