Abstract Carotenoid-based coloration is a well-documented example of a condition-dependent trait, but much of the evidence supporting condition dependence of red carotenoid coloration comes from species that color their feathers primarily with 3-hydroxyechinenone, a red carotenoid produced from yellow dietary carotenoids via an unknown pathway. The condition dependence of red plumage in species that use the more common CYP2J19 and BDH1L enzymes to modify dietary yellow carotenoids into red ketocarotenoids is less well studied. We tested the hypothesis that captivity would negatively affect production of red pigments by male Cardinalis cardinalis (Northern Cardinal), a songbird with extensive red coloration produced via the CYP2J19/BDH1L pathway. We confined a group of wild-caught male cardinals in cages during molt, using captivity as a physiological challenge, and compared them to free-living cardinals. We provided captive birds with abundant zeaxanthin and lutein, the dietary yellow pigments that cardinals enzymatically convert into the red ketocarotenoids astaxanthin and α-doradexanthin, to ensure that insufficient carotenoid access would not limit production of red pigments. During molt, we measured concentrations of carotenoid pigments in the plasma and growing feather follicles of both captive and free-living cardinals. Compared to free-living cardinals, captive birds had significantly lower relative concentrations of red carotenoids in both follicles and plasma. The observation that, compared to free-living cardinals, captive male cardinals showed reduced production of red carotenoids with lower quantities in feather follicles supports the hypothesis that red coloration produced via the CYP2J19/BDH1L pathway is a condition-dependent trait.
Patton et al. (Mon,) studied this question.