Melanin and carotenoid ornaments are related to the individual condition in free-living grey partridges (Perdix perdix)

Abstract

According to the viability indicator hypothesis, ornaments of many bird species honestly signal individual quality and health status. In this study, we investigated the health- and stress-indicating capacity of both feather- and skin-based ornamental traits in the grey partridge (Perdix perdix), a vulnerable avian species of the European agricultural landscape. In 50 free-living males, we assessed individual health status by examining the differential and absolute leukocyte counts, absolute erythrocyte count, complement activity, and pro-inflammatory immune responsiveness to phytohaemagglutinin (PHA). We found that males expressing extensive melanin-pigmented breast ornaments developed stronger skin inflammation after PHA stimulation than males with limited ornaments, suggesting that these are high-quality individuals that are able to mount a robust immune response. Furthermore, we found that the UV signal of the carotenoid-pigmented eye patch ornament is negatively related to the absolute immature erythrocyte count and the peripheral blood heterophil/lymphocyte (H/L) ratio, indicating that males with a slow pace of life and healthier males express skin ornaments with higher UV reflectance. Ornamental colouration in grey partridge males may, therefore, serve as a reliable signal of condition (in terms of resource balance) and health (in terms of stress resistance) to females.