An outbreak of avian flu that has been spreading across the United States and Canada over the past six months only seems to be getting worse. First appearing in Canada last fall, the flu has ravaged industrial flocks and has now been detected in a wide variety of North American wild birds, raising alarms among ecologists. A particularly virulent strain known as highly pathogenic avian influenza A (H5N1), or HPAI, the flu has already killed millions of domestic North American fowl, according to the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS). To date, more than 28 million domestic poultry in 29 states have died either through infection or preventative culling. In Canada, seven provinces have detected the virus in commercial and backyard poultry. The flu has also appeared in wild flocks in unprecedented numbers, with more than 700 positive birds collected from 31 states and nine Canadian provinces—numbers that indicate a...