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 Migratory birds have been implicated in the distribution of the highly pathogenic avian influenza (HPAI) H5N1 virus (Chen et al. 2005, Normile 2005a, Normile 2005b, Normile 2006). Understanding migration strategies is essential in examining the role of wild birds in the spread of avian influenza and in predicting transmission routes within and across continents. Migratory birds follow certain general directions, most often north-south movements, from winter habitats to nesting areas and return travel to their post-nesting quarters. These “routes” are not necessarily an exact course made by individual birds or a path followed by a species with specific geographic or ecological boundaries (Lincoln 1979). Alaska is unique because four major flyway systems—East Asia/Australasia, Central Pacific, Pacific Americas, and Mississippi Americas—overlap creating a crossroads for many species (see Flyways of the World figure). This overlap establishes a path for potential disease transmission across continents and for mixing, re-assortment, and exchange of genetic material among strains of avian influenza from Eurasia and North America (see Flyways of North America figure).
The bar-tailed godwit (Limosa lapponica) is an example of a migratory species that crosses several flyways during its annual cycle (see figure). The entire Alaska-breeding race of the bar-tailed godwit migrates through the East Asian/Australasian flyway. It has an extraordinary, long distance migration of up to 11,000 km from staging areas in western Alaska to wintering habitats in New Zealand and Australia (see figure; Gill et al. 2005). The bar-tailed godwit is a high priority species to sample for HPAI because migrants arriving in Alaska to nest each spring are just days removed from their staging sites along the coast of eastern Asia (see figure) where the H5N1 virus has been isolated.
Chen, H., G.J.D. Smith, S.Y. Zhang, K. Qin, J. Wang, K.S. Li, R.G. Webster,
J.S.M. Peiris, and Y. Guan. 2005. H5N1 virus outbreak in migratory waterfowl. Nature 436:191-192. PDF file 158 kb
Gill, R.E., Jr., T. Piersma, g. Hufford, R. Servranckx, and A. Riegen. 2005.
Crossing the ultimate ecological barrier: evidence for an 11,000-km-long nonstop flight from Alaska to New Zealand and eastern Australia by
bar-tailed godwits. Condor 107:1-20. PDF file 940 kb
Lincoln, F.C. 1979. Migration of birds. U.S. Fish and Wildlife Service, Circular
16, Washington, D.C.
Normille, D. 2005a. Potentially more lethal variant hits migratory birds in China. Science 309:231. PDF file 11.1 mb
Normile, D. 2005b. Are wild birds to blame? Science 310:426-428. PDF file 2.56 mb
Normile, D. 2006. Evidence points to migratory birds in H5N1 spread. Science 311:1225. Normile, D. 2005a. Potentially more lethal variant hits migratory birds in China.
Science 309:231. PDF file 145 kb
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North American Flyways
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Bar-tailed Godwit Migration Route |
World Flyways |
Bar-tailed Godwit Migration Map
PDF file 1.4 mb
(see Gill et al. 2005 for reference) |
Approximate numbers of migrant birds that move between Asia and Alaska
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