Fault bars and bacterial infection
Fault bars are conspicuous malformations on bird feathers that are produced during feather growth. The causes of fault bars are poorly understood. In our study, we used the presence of Campylobacter jejuni infection in 302 urban feral pigeons (Columba livia) as a proxy of physiological stress and correlated this stress with fault bar abundance. The overall prevalence of Campylobacter infection in these birds was 24.5 %. Bacterial infection was equally prevalent in young birds and adults, but males showed a slightly higher prevalence than females. Fault bars were more abundant in young birds than in adults, particularly among young males. Pigeons with Campylobacter infection had more fault bars than uninfected birds. These results suggest that the physiological state of the individual bird could be as important as external stressors in determining the occurrence of fault bars and that parasites may play a role in fault bar formation.