In 2023, H5N1 avian flu killed nearly all seal pups and many adults in Argentina’s Península Valdés, marking a deadly spillover from birds to marine mammals.

In 2023, a deadly outbreak of the H5N1 avian influenza virus devastated a southern elephant seal colony on Argentina’s Península Valdés, killing nearly all seal pups and many adults. The virus, previously seen in birds, jumped to marine mammals and spread through sustained mammal-to-mammal transmission along the coast, causing unprecedented mortality. Pup survival dropped from 4,145 in 2022 to just 135 in 2023, with widespread disruption to breeding behaviors and social structures. Scientists say climate change, habitat loss, and human activity are increasing the risk of such spillover events, posing growing threats to wildlife and public health.