Figure 2. Number of nest boxes, in all three test groups, with BFDV-positive nest swabs before, during and after breeding, and percentage of BFDV-positive nest swabs in nests with BFDV-positive adults or nestlings, and BFDV shedding parents, during the breeding season.

(A) number of nest boxes (out of total of 33 for the three test groups, 11 per group) with BFDV-positive nest box swabs before, during and after the breeding season, analysed with detection threshold ₃₆. For unoccupied nest boxes during the breeding season, the sample size was 10 instead of 11. (B) percentage of nest boxes with BFDV-positive (‘BFDV+’) nest swabs ± 95% confidence intervals, which were occupied by BFDV shedding parents (as detected with HA; only females could be tested for shedding, see Materials & Methods), by BFDV-positive parents, or by BFDV-positive nestlings (as detected with qPCR of blood samples), during the breeding season. Shedding parents are also BFDV-positive as detected by qPCR, and are also part of the bar showing ‘nests with BFDV+ parent’. The number at the base of bars indicates number of nest boxes with BFDV-positive nest box swabs out of the total number of nest boxes occupied by BFDV-positive or shedding parents or nestlings.