Genetics, local environment and health as factors influencing plasma carotenoids in wild American kestrels (Falco sparverius)

Carotenoids are important as pigments for bright: coloration of animals, an d as physiologically active compounds with a wide array of health-related f unctions. Carotenoid-dependent coloration may have evolved as a signal to c onspecifics; however, factors that may limit availability of carotenoids ar e poorly known. We investigated how the acquisition of carotenoids may be c onstrained by availability in the environment, diet, genetic make-up and he alth status of wild American kestrels (Falco sparverius). Plasma concentrat ions of siblings at the time of fledging showed a high degree of resemblanc e; however, a cross-fostering experiment revealed that variance was largely explained by nest of rearing, rather than nest of origin, thus indicating a low genetic component. A multivariate analysis of attributes of nestlings (sex, size, plasma proteins, immune function), parental reproduction (layi ng date, clutch size) and rearing conditions (brood size, size hierarchy ne stling mortality) showed only a small significant effect of leucocyte diffe rentials on carotenoid concentrations of nestlings. A strong environmental effect on plasma carotenoids was demonstrated by levels of adult kestrels b eing correlated within mated pairs, and having a significant association wi th the abundance of voles, the primary prey species, per territory.