Colour of adult avian integumentary features reveals differences related to in ovo stressors

Abstract

Developmental stress experienced during the embryonic period has the potential to affect individual quality and to exert long‐term impacts on avian fitness. Avian integumentary characteristics such as skin and feather colour (potential markers of red‐related carotenoid pigmentation or black‐related melanin pigmentation) can affect mate selection and reproductive investment in the wild and can act as honest signals where the level of colour expression correlates with genetic, nutritional or environmental ‘quality’ of the individual. However, little is known about whether embryonic conditions and stressors experienced in ovo persist to affect integumentary adult feather and skin coloration. In this study, we used digital photography measures of eye‐ring and breast‐band colour, structural body size, feather corticosterone, and moult progression to assess whether temperature and contaminant stress experienced by embryos later impacts ornament expression in 1‐year‐old captive‐reared Killdeer Charadrius vociferus. Study birds had been previously exposed to polychlorinated biphenyl (PCB) 126 or DMSO (control) at different incubation temperatures (36, 37.5 and 39 °C) in ovo but were subsequently hatched and reared under identical conditions. We found corticosterone levels at hatch from Killdeer tail feathers were higher in response to increased incubation temperature (but not to PCB exposure), suggesting adrenal activity was affected by temperature during the sensitive in ovo period. Digital photography detected individual differences in integumentary colour that covaried with temperature treatment and feather corticosterone at hatch. Birds with higher feather corticosterone levels had chromatically blacker breast‐bands as adults and exhibited signs of earlier moult, structurally shorter tarsi, and longer head bill and culmen. Birds incubated below optimal temperature had chromatically more yellow (less orange) eye‐rings. Overall, we found that digital photography revealed differences in breast‐band and eye‐ring colour and that these variations in integumentary traits can reflect persistent differences in individual size and quality resulting from early life temperature stress.