The H5N1 strain of avian flu is now passing easily among South America's elephant seals and drastically cutting herd populations, a new report finds.

In 2023, a highly pathogenic bird flu leapt to seals in South America, killing some 17,000 elephant seal pups (about 97 percent of the vulnerable animals) and an unknown number of adults in a major breeding colony in Península Valdés,

A year after an outbreak of H5N1 killed thousands of elephant seals, only about a third of the seals normally expected here returned, UC Davis scientists and partners estimate. A study chronicles the 2023 outbreak.

The sea mammals' population may slowly rebound, but in 2023 mutant bird flu killed an estimated 17,000 elephant seals, including about 97% of their pups, researchers reported Nov. 11 in Nature Communications.