The H5N1 bird flu virus, which has caused significant outbreaks in dairy cows in the U.S., is showing increased adaptability to spread in mammals. Researchers have found evidence of the virus spreading among elephant seals and other marine mammals in South America. This raises concerns that the virus could eventually transmit from mammal to mammal and potentially pose a threat to humans. Genetic sequencing has identified a particular lineage of the virus that has evolved to spread easily between mammals. This lineage has been linked to outbreaks in multiple countries in South America, marking the first known multinational mammal-to-mammal spread of the virus. Scientists emphasize the need for continued monitoring of the virus in wildlife to understand its potential implications for human health.