Carotenoids are important as pigments for bright coloration of animals, and as physiologically active compounds with a wide array of health–related functions. Carotenoid–dependent coloration may have evolved as a signal to conspecifics; however, factors that may limit availability of carotenoids are poorly known. We investigated how the acquisition of carotenoids may be constrained by availability in the environment, diet, genetic make–up and health status of wild American kestrels (Falco sparverius). Plasma concentrations of siblings at the time of fledging showed a high degree of resemblance; 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 (laying date, clutch size) and rearing conditions (brood size, size hierarchy, nestling mortality) showed only a small significant effect of leucocyte differentials on carotenoid concentrations of nestlings. A strong environmental effect on plasma carotenoids was demonstrated by levels of adult kestrels being correlated within mated pairs, and having a significant association with the abundance of voles, the primary prey species, per territory.