How annual bird migration could spread avian flu

Scientists are still trying to understand exactly how a virulent bird flu is spreading through farms in the United States, but one pattern is clear: poultry and cows risk exposure to sick wild birds migrating across the Americas. One way to understand the relationship between migrating birds and agricultural livestock is to look at the path of the mallard duck which has the most recorded avian flu infections. January Mallards spend winters across the United States. As they migrate north for the breeding season, the mallards pass over chicken farms big and small. April They may use farms as a water and food source throughout their journey. “Outbreaks among poultry are more likely to happen where migratory waterfowl are present,” said Claire Teitelbaum, a researcher with Bay Area Environmental Research Institute. July In the breeding season, birds return to cooler landscapes that may still contain viruses from a previous season. A virus can persist for weeks or months in colder environments, meaning birds could contract multiple virus variants. Those variants can undergo genetic changes that enable the virus to infect new species. September Viruses travel along bird migration routes or “flyways,” transferring from one wild bird to another. While only