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

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.

Correlation of Cere Color with Intra- and Interspecific Agonistic Interactions of Crested Caracaras

“…Leg colors do change non-facultatively with age, from pale blue as nestlings, to pale yellow as juveniles, to dark yellow as adults (Morrison and Dwyer 2012). Pooling slight differences in cere color corrected for variability in interpretation of cere colors among observers, corrected for differences in the base color of the integument of individual birds, and grouped birds into categories of flushed and not flushed consistent with previous studies of facial flushing in raptors (Negro et al 2006, Bamford et al 2010, Blanco et al 2013.…”

“…If true, then cere colors characteristic of individuals at rest (passively avoiding agonistic interactions), might also be displayed by individuals seeking to be at rest (actively avoiding agonistic interactions), consistent with my observations. In contrast, Lappet-faced Vultures display dark heads when aggressive and light heads when subordinate (Bamford et al 2010), and Andean Condors show bare skin full of blood when dominant (Blanco et al 2013). Apparently, superimposition of a signaling system on a thermoregulatory process does not require evolution of identical signaling conventions among convergently evolved species.…”

“…Thus, correlations between cere color and roles during agonistic interactions had been hypothesized but not previously investigated. I predicted that if a signaling hypothesis is correct, cere color of the participants in agonistic interactions should be correlated with the role of participants in interactions (as in Bamford et al 2010, Blanco et al 2013. I found cere colors were consistently light across age classes when caracaras acted as the aggressors in intraspecific or interspecific agonistic interactions and consistently dark when caracaras were receivers of intraspecific or interspecific aggression.…”

“…Individuals displaying deep red skin consistently win intraspecific agonistic interactions with individuals displaying pink skin. As signals of dominance in feeding hierarchies, Andean Condors (Vultur gryphus) change the color of bare skin on the head from pale pink, yellow, or grey to deep yellow, orange, or red within a few seconds during contests at carcasses (Blanco et al 2013). Also during contests at carcasses, Hooded Vultures (Necrosyrtes monachus) facultatively change the skin color of their mostly un-feathered heads from pink to purplish-red during intraspecific interactions (Negro et al 2006).…”

“…Negro et al (2006) hypothesized cere color could serve as a quick and quickly reversible signal visible to nearby conspecifics, but the hypothesis has not been quantitatively investigated in wild caracaras. I predicted that if a signaling hypothesis is correct, cere colors displayed by participants in agonistic interactions should be correlated with the role of participants in interactions (as in Bamford et al 2010, Blanco et al 2013). …”