Sex-and age-related variation in plasma carotenoids despite a constant diet in the Red-legged Partridge Alectoris rufa

We studied seasonal variation in plasma carotenoid levels of captive Red-le gged Partridges Alectoris rufa in relation to sex, age and condition. The l egs, bill and eye lores in this species are bright red due to carotenoid pi gments. Carotenoid levels in the plasma varied significantly among sampling periods. Males presented higher values than females of their same age grou p, except in the last sampling period in summer. Adult partridges (2-year o ld) presented significantly higher carotenoid levels than first-year birds at the beginning of the study, but this age effect was not constant through out the season. The sex-specific variation in plasma carotenoids cannot be attributed to diet, as this was the same for all individuals across the stu dy. Body mass, and thus condition, did not change significantly across the study, and was therefore not related to seasonal variation in plasma carote noids. These results imply physiological regulation of carotenoids, opposit e to a direct relationship among carotenoid content in the diet and colour expression in the integument, as suggested in some previous studies.