The widespread practice of reusing chicken manure as a fertilizer for fish farms, a practice promoted by aquaculturalists, may be responsible for transmitting H5N1 virus from infected poultry to wild birds. While we don't know enough yet about how widespread this practice is, and have mostly circumstantial evidence to support the case of viral transmission this way (the Mute Swan that died of H5N1 avian influenza in Croatia was found at a fish farm), there does seem to be a viable risk here to wild birds.
Again, there is a lot we need to learn about this virus and how it is transmitted. For now, transmission from wild birds seems to be the least of our worries (there haven't been repeated huge die-offs of wild birds in Asia, and no confirmed cases of domestic birds getting the virus from wild birds). Meanwhile, several outbreaks in wild birds may be caused by exposure to infected poultry, so poultry raising and marketing practices need to be more closely studied so we can get a better idea of what is really going on.