Abstract
Among birds, vultures show low concentrations of plasma carotenoids due to the combination of their large size, general dull colouration and a diet based on carrion. We recorded the concentration of each carotenoid type present in plasma of the Andean condor (Vultur gryphus) according to age and sex, that determine colour signalling and dominance hierarchies in the carcasses. We compared the carotenoid profile in wild condors with that of captive condors fed with a controlled diet of flesh to test the hypothesis that wild individuals could acquire extra carotenoids from vegetal matter contained in carcass viscera and fresh vegetation. Wild American black vultures (Coragyps atratus) were also sampled to evaluate the potential influence of colouration in the integument on absorption and accumulation patterns of plasma carotenoids. A remarkably higher concentration of lutein than β-carotene was found in wild condors, while the contrary pattern was recorded in American black vultures and captive condors. We found a consistent decrease in all plasma carotenoids with age, and a lower concentration of most xanthophylls in male compared to female wild condors. Positive correlations of all carotenoids indicated general common absorption and accumulation strategies or a single dietary source containing all pigments found in plasma. The comparatively low total concentration of carotenoids, and especially of lutein rather than β-carotene, found in captive condors fed with a diet restricted to flesh supports the hypothesis that Andean condors can efficiently acquire carotenoids from vegetal matter in the wild. Andean condors seem to be physiologically more competent in the uptake or accumulation of xanthophylls than American black vultures, which agrees with the use of colour-signalling strategies in sexual and competitive contexts in the Andean condor. This study suggests that vultures may use dietary vegetal supplements that provide pigments and micronutrients that are scarce or missing in carrion.
Highlights
Carotenoids play important roles in the production of coloured signalling traits and health maintenance by acting as provitamin A, immunomodulators, antioxidants and photoprotectants [1,2,3]
The carotenoid profiles were qualitatively similar in Andean condors and American black vultures captured in the same area and on the same dates (Fig. 2), as well as in captive Andean condors (Table 1)
We found an unexpectedly large variety of carotenoids in plasma of Andean condors and American black vultures, two scavengers that mostly feed on herbivore mammal carcasses in varying states of decomposition [24,25,30]
Summary
Carotenoids play important roles in the production of coloured signalling traits and health maintenance by acting as provitamin A, immunomodulators, antioxidants and photoprotectants [1,2,3]. Animals obtain carotenoids from the food-chain as these pigments are only synthesized by primary producers [4]. It has been proposed that these pigments are limiting resources in the attainment of colouration due to general environmental constraints and the low availability and accessibility of carotenoids in food [3]. This potential limitation can promote trade-offs in the maintenance of honest condition-dependent colouration [9,10], the production of carotenoid-dependent ornamentation could be linked to the biochemical efficiency of vital cellular processes [3]. Whatever the ultimate cause or mechanisms of carotenoid allocation, the uptake of these pigments should be proximately determined by the degree to which carotenoids are limiting and by the individuals’ ability to obtain them from their diet [5,11,12]
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