Despite disagreement about the role of fly-ways in limiting viral spread among wild birds (17,18), therapid spatial diffusion and transmission of HPAIV in wildand domestic birds highlight the need to further investigatethe processes involved in viral emergence and spread.

The timing and direction of this virus’sdissemination, which coincided with waterfowl migra-tion patterns, together with phylogenetic and geospatialdata (3,4) support the hypothesis that Gs/GD H5N8 clade2.3.4.4 was introduced into North America through theBeringian Crucible via intercontinental movement ofmigratory waterfowl (5,6).