Antibodies detected by ELISA during challenge in falcons. Antibodies of all groups detected by the ID Screen© WN competition ELISA (IDVet, Grabels, France) during the challenge period are shown. Optical density at 450 nm is converted to signal/noise% (S/N%) ratio (S/N% = ODsample/ODnegative control * 100), with values ≤ 40% considered positive, >40% and ≤50% equivocal and >50% negative. The threshold for positive results is indicated as a solid red line. In box-and-whisker plots, the ends of the whiskers represent the minimum and maximum values, respectively. Outliers are represented as black dots instead of whisker-ends and the box includes 50% of the values for each group.