California migration of millions of birds brings ‘unprecedented’ avian flu threat

Ever year during the fall migration season, 5.4 million waterfowl descend on California, as birds from Canada and Alaska make their way south on an aerial transnational highway known as the Pacific Flyway.

This year, the arrival of the birds also brings concern. A new avian influenza is circulating, and that means trouble for domestic chickens, wild birds and even mammals.

"The prediction is we're going to be hammered in the next several months," said Maurice Pitesky, who monitors and forecasts bird viruses at the University of California, Davis.

There are 144 known types of bird viruses, most of them mild. Just as human viruses do, they swirl around the world and pop up in different places.

This year's flu, known as H5N1, came from Europe, scientists say. Since its first detection in the US in January, in a wild duck in North Carolina, the high-pathogenic virus has spread rapidly across the country. In California, the strain was first recognized in geese and pelicans in the Central Valley in July of this year. Since then, more than 10 counties in the state have documented cases.

"Geographically speaking, we're dealing with something unprecedented," Pitesky said. "It's only going to speed up over the next couple of months."

The most recent bad flu year for birds in North America was 2014-15, when 50 million chickens and turkeys were killed, either from the virus itself or culled to stop the flu from advancing - something known in the poultry industry as depopulation.