A newly arrived bird flu is sweeping through wild bird populations in the United States, and that may mean trouble for poultry farmers who have been doing their best to control this flu outbreak in their flocks. Some 24 million poultry birds like chicken and turkeys have already been lost, either because they died from the virus or were killed to prevent its spread. But unlike a similar bird flu outbreak seven years ago, this one is unlikely to just burn itself out. That’s because this particular flu virus seems capable of hanging around in populations of wild birds, which...