Washington ? Ducks have a flu season just like people do – and they’re more likely to be sick in the fall than in the spring.

So authorities must keep their guard up even if the government’s mass testing of migrating birds, beginning now in Alaska, doesn’t spot the worrisome H5N1 bird-flu strain right away.

That’s a key warning from a new review, being published today, of what scientists know – and don’t know – about how waterfowl constantly incubate influenza, and how much of a role wild birds play as this deadly new flu strain hopscotches around the globe.

And it’s one that federal wildlife officials are taking into account as they determine how many birds to test now, as ducks and other migratory species start flying into Alaska’s breeding grounds from Asia, and how many to test later in the year.