The Grain report on global poultry industry and H5N1 looks excellent to me. http://www.grain.org/briefings/?id=194#_ftn31 (see thread here re farming and H5N1)

Includes mention re contaminated feed being thought to be a source of H5N1.
“The global trade in poultry feed, another factor in this whole mess, is dominated by the same companies. One of the standard ingredients in industrial chicken feed, and most industrial animal feed, is “poultry litter”. This is a euphemism for whatever is found on the floor of the factory farms: fecal matter, feathers, bedding, etc.[43] Chicken meat, under the label “animal by-product meal”, also goes into industrial chicken feed.[44] The WHO says that bird flu can survive in bird faeces for up to 35 days and, in a recent update to its bird flu fact sheet, it mentions feed as a possible medium for the spread of bird flu between farms.[45] Russian authorities pointed to feed as one of the main suspected sources of an H5N1 outbreak at a large-scale factory farm in Kurgan province, where 460,000 birds were killed.

So, got me wondering: is it possible that in areas where swans evidently dispersed from, they could have eaten contaminated feed?
Not sure if maybe poultry feed dumped as suspect (what happened to rest of the feed in Kurgan province, after problems surfaced, say?); or are there refuges where birds are fed in winter, as in some UK reserves?

Might help explain preponderance of mute swans, if directly fed (for some infections at least).