Figure 4.

Proportion of viruses from the North American clade of avian influenza virus among wild bird isolates (blue) or poultry outbreaks (pink) in North America (A) or Eurasia (B). All poultry outbreaks in Eurasia were caused by viruses from the Eurasian clade (results not shown). Wild bird isolates are grouped by decade. Black circles show proportions of all isolates per decade (number of isolates per decade shown next to circles), black lines show fitted logistic regressions, and red circles show individual poultry outbreaks.