Parasites, condition, immune responsiveness and carotenoid‐based ornamentation in male red‐legged partridge Alectoris rufa

Sexual ornaments might indicate better condition, fewer parasites or a greater immune responsiveness. Carotenoid-based ornaments are common sexual signals of birds and often influence mate choice. Skin or beaks pigmented by carotenoids can change colour rapidly, and could be particularly useful as honest indicators of an individual's current condition and/or health. This is because carotenoids must be acquired through diet and/or allocation for ornamental coloration might be to the detriment of self-maintenance needs. Here, we investigated whether the carotenoid-based coloration of eye rings and beak of male red-legged partridges Alectoris rufa predicted condition (mass corrected for size), parasite load (more specifically infection by coccidia, a main avian intestinal parasite) or a greater immune responsiveness (swelling response to a plant lectin, phytohaemagluttinin, or PHA). Redness of beak and eye rings positively correlated with plasma carotenoid levels. Also, males in better condition had fewer coccidia, more circulating carotenoids and a greater swelling response to PHA. Carotenoid-based ornamentation predicted coccidia abundance and immune responsiveness (redder males had fewer coccidia and greater swelling response to PHA), but was only weakly positively related to condition. Thus, the carotenoid pigmentation of beak and eye rings reflected the current health status of individuals. Our results are consistent with the hypothesis that allocation trade-offs (carotenoid use for ornamentation versus parasite defence needs) might ensure reliable carotenoid-based signalling.