Bird flu experts see a familiar threat — and an unpredictable virus

A pelican suspected to have died from H5N1 avian influenza is seen on a beach in Lima

Tracking the bird flu, experts see a familiar threat — and a virus whose course is hard to predict

While scientists who have been studying H5N1 bird flu for a couple of decades have a very healthy respect for it, a number are hedging their bets about what the virus’s future path will look like.