The authors conclude that:
HPAI H5N1 spread rapidly across Eurasia during 2005 for reasons that are not entirely understood. Despite this rapid movement, effective introduction (i.e., under conditions allowing its spread) of the virus to the New World through migratory or vagrant birds seems unlikely. Few individual members of few waterfowl species migrate between hemispheres, and should a bird make the journey while shedding sufficient active virus to infect birds in the Western Hemisphere, newly infected birds would probably die before being able to transport the virus from the entry site. If spread of HPAI H5N1 to the New World occurs in its current form (e.g., through domestic or pet bird trade or smuggling), it should be readily detectable because of the large number of dead native birds likely to result.
Reference: Rappole, J.H. and Hubálek, Z. (2006) Birds and influenza H5N1 virus movement to and within North America. Emerging Infectious Diseases, October 2006 issues, available online at: http://www.cdc.gov/ncidod/EID/vol12no10/05-1577.htm