JohnInKansas, it would appear that the presence of influenza virus in wild birds has been known since 1961.

"The first isolation of influenza virus from feral birds was in 1961 from common terns (Sterna hirundo) in South Africa (4), but it was not until the mid-1970s that any systematic investigation of influenza in feral birds was undertaken. These revealed the enormous pools of influenza viruses now known to be present in the wild bird population."

Further studies were done in the 80's.

"Virus isolations from other wild birds have been completely overshadowed by the number, variety and widespread distribution of influenza viruses in waterfowl, Order Anseriformes.

In the surveys listed by Stallknecht and Shane (5) a total of 21,318 samples from all species resulted in the isolation of 2,317 (10.9%) viruses. Of these samples 14,303 were from birds of the Order Anseriformes and yielded 2,173 (15.2%) isolates. The next highest isolation rates were 2.9% and 2.2% from the Passeriformes and Charadriiformes and the overall isolation rate from all birds other than ducks and geese was 2.1%"