In three decades of working with elephant seals, Dr. Marcela Uhart had never seen such a sight on a beach on Argentina's Valdes Peninsula last October.
It was peak breeding season; The beach should have been filled with harems of fertile females and huge males fighting each other for dominance. Instead, it was "just carcasses upon carcasses," recalls Dr. Uhart, who directs the Latin American Wildlife Health Program at the University of California, Davis.
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cdH5N1, one of the many viruses that cause bird flu, has already killed at least 24,000 South American sea lions off the continent's coast in less than a year. Now it came for the elephant seals.
Chicks of all ages, from newborn to fully weaned, are dead or dying at the high tide line. Sick puppies lie down, foaming at the mouth and nose.
Dr. Uhart calls it "a picture of hell."
In the weeks that followed, he and a colleague — protected from head to toe in gloves, gowns and masks, and periodically dousing themselves in bleach — meticulously documented the devastation. Team members stand atop a nearby hill and assess the toll with a drone.
What they found was staggering: the virus had killed an estimated 17,400 seal pups, more than 95 percent of the colony's young animals.
The disaster is the latest in a bird flu epidemic that has swept the world since 2020, prompting authorities on multiple continents to kill millions of poultry and other birds. In the United States alone, more than 90 million birds have been killed in a futile attempt to contain the virus.
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cdThere has been no stopping H5N1. Avian flu viruses are selective about their hosts, usually sticking to one type of wild bird. But it quickly infiltrated a surprisingly wide range of birds and animals, from squirrels and skunks to bottlenose dolphins, polar bears and, more recently, dairy cows.
"In my flu career, we've never seen a virus that expands its host range like this," said Troy Sutton, a virologist at Penn State University who studies avian and human influenza viruses.
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