Blue-winged teal, a species related to ducks, is among the first species to fly south in the fall. In mid-September, three hunter-harvested teals tested positive for the virus in Mississippi, marking the first discoveries in that state. The finding confirms that: “Yes, the virus persisted all summer in northern latitudes,” said Mr. Richards. “And it comes back on the wings of wild waterfowl.”
Wisconsin began to see a spike in wild bird infections around Labor Day, said Dr. Poulsen, and recently documented the first poultry outbreaks since May. “We really hoped we were out of the woods,” he said.
The virus appears to be making a comeback in other northern regions, including Minnesota, North Dakota and Alberta, Canada. So far, experts have said, the increase has been smaller than in the spring. “But there are many more geese and ducks coming from the Arctic,” said Margo Pybus, a provincial wildlife specialist with Alberta’s Fish and Wildlife Division.
Further south, wildlife facilities are preparing for a flood of autumn migrants. Southern California was spared in the spring, but Dr. Hendrik Nollens, the vice president of wildlife health at the San Diego Zoo Wildlife Alliance, doesn’t expect to be so lucky this fall.
The San Diego Zoo and its sister facility, the San Diego Zoo Safari Park, covered their outdoor aviaries and removed food and water sources that could attract bird intruders, even going as far as draining a pond popular with mallards. They also moved 900 birds to more protected habitats — “a huge effort” that involved moving hundreds of flamingos, said Dr. nollens.
To accomplish the feat, employees led many of the flamingos into enclosed trailers, which transported the animals to covered or indoor habitats. Workers adapted these new spaces to accommodate the long-legged waders, adding feeding basins, pruning low-hanging tree branches and raising sprinklers designed to keep their feathers in good condition.
It is unclear when the flamingos will return home. “When do we stop doing these things is actually a tough challenge,” said Dr. nollens. “We don’t know what will happen from here.”
