Avian influenza A virus (AIV) has threatened global economy and public health. Wild birds have long been thought to serve as the natural reservoir of influenza virus, and thus it is expected that wild birds harbor higher viral diversity than poultry. Yet, this hypothesis has not been formally tested. Here, we assemble a data set of AIV from 75 regions worldwide over 11 years and compare the genetic diversity of wild bird AIV with that of poultry AIV. We find the genetic diversity of the internal genes of AIV in wild birds is not significantly higher than that in poultry. We propose that the unexpected diversity pattern of AIV internal genes could be explained by the synchronized global sweep of AIV internal genes occurring in the late 1800s and frequent AIV transmission between wild birds and poultry. Our findings might have important implications in understanding the evolution of influenza virus.