The wild bird route is promoted again, this article based on a Science paper is on the front page of BBC news:
http://www.bbc.co.uk/news/science-environment-31139263
http://www.sciencemag.org/content/347/6222/616.summary?sid=df6e460f-fb77-455f-9d8e-dc91fb73aa60
But reading it there is no actual evidence, just speculation; in particular someone ought to be asked to explain the arrow from Russia to sub-Saharan Africa – which species of wildfowl follow this route? Of course there are none…