Paper just out in which migrations of Bewick's swans were followed. Two birds with low path (non lethal) bird flu travelled more slowly than healthy birds, evidently as their bodies dedicated resources to fighting the illness.
Our observations that infection of swans with such “ordinary” LPAI H6 viruses can result in altered migratory and feeding patterns may indicate that LPAI virus infections in wild birds have a higher clinical, epidemiological, and ecological impact than previously recognised. Based on these observations, the implications of influenza virus infections, including those caused by HPAI H5N1 viruses, for bird health and ecology and virus epidemiology may require re-evaluation.
Hampered">http://dx.doi.org/10.1371/journal.pone.0000184]Hampered Foraging and Migratory Performance in Swans Infected with Low-Pathogenic Avian Influenza A Virus - note that H5N1 variants of concern (aka poultry flu) tend to kill hosts, and as noted on this site, Dead Ducks Don't Fly.