Avian nuptial plumage coloration changes differently when exposed to urban and rural areas

AbstractAvian plumage coloration could be altered by external factors like dust accumulation, but the effect of environmental conditions on such post-moult colour changes are poorly studied. Here, we investigated how exposure to the atmosphere in habitats of differing anthropogenic pressures modifies UV/blue structural plumage coloration- a sexually-selected trait in Eastern BluebirdsSialia sialis. We collected feather samples from live birds and distributed them in three types of habitats: i) urban roads with low traffic, ii) urban roads with high traffic, iii) rural roads with low traffic. After 4 weeks, the brightness of feathers decreased in all types of habitats-resulting in less-ornamented coloration. Changes in UV and blue chroma, however, varied with habitat type; chroma decreased in urban areas (becoming less ornamented), but increased in rural locations (becoming more ornamented). According to physiological models of avian colour vision, however, these changes in coloration tended to be below perceptual thresholds. Our results underscore the importance of how human activity can influence plumage colour of individual birds during the period between moult cycles which could have an impact on avian visual signaling. The study opens venues for further studies focusing on how the optical properties of specific airborne particles can influence coloration of wild-living animals.