Need and Seek for Dietary Micronutrients: Endogenous Regulation, External Signalling and Food Sources of Carotenoids in New World Vultures

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.

在鸟类类群中，秃鹫因体型庞大、通体羽色暗沉且以腐肉为食，其血浆类胡萝卜素（plasma carotenoids）浓度普遍偏低。我们依据年龄与性别两个影响腐食场景下体色信号传递与优势等级秩序的因素，检测了安第斯神鹫（Andean condor，Vultur gryphus）血浆中各类类胡萝卜素的浓度。我们将野生安第斯神鹫的类胡萝卜素谱与饲喂可控纯肉日粮的圈养安第斯神鹫进行对比，以此验证假说：野生个体可从腐尸内脏与新鲜植被所含的植物性物质中获取额外的类胡萝卜素。我们还对野生美洲黑鹫（American black vulture，Coragyps atratus）进行了采样，以评估体表着色对血浆类胡萝卜素吸收与积累模式的潜在影响。研究发现，野生安第斯神鹫体内叶黄素（lutein）的浓度显著高于β-胡萝卜素（β-carotene），而美洲黑鹫与圈养安第斯神鹫则呈现出完全相反的模式。我们还观察到，所有血浆类胡萝卜素的浓度均随年龄增长呈持续下降趋势；且相较于雌性野生安第斯神鹫，雄性个体体内多数叶黄素类（xanthophylls）的浓度更低。各类类胡萝卜素间均呈正相关关系，这表明野生神鹫要么存在共通的吸收与积累策略，要么其单一膳食来源便包含了血浆中检出的所有色素。饲喂纯肉日粮的圈养安第斯神鹫体内类胡萝卜素总浓度相对偏低，尤其是叶黄素浓度远低于β-胡萝卜素，这一结果支持了"野生安第斯神鹫可高效从植物性物质中获取类胡萝卜素"的假说。相较于美洲黑鹫，安第斯神鹫在叶黄素类的摄取或积累方面生理能力更强，这与其在性选择与竞争场景中运用体色信号策略的现象相符。本研究表明，秃鹫可通过摄取膳食中的植物性补充物，获取腐食中稀缺或缺失的色素与微量营养素。