EVects of carotenoid supplementation on colour expression, oxidative stress and body mass in rehabilitated captive adult kestrels (Falco tinnunculus)

Carotenoids are considered a limited resource for animals because they are not synthesised by the body. Birds use carotenoids, mainly xanthophylls, for physiological functions, such as anti-oxidant activity, and for colour expression; hence, they need to shunt carotenoids between competitive demands. Recent studies suggest that the antioxidant role of xanthophylls might not be as important as previously thought and that at high concentrations they may, in fact, acquire pro-oxidant properties. In this work, we studied the eVects of a moderate xanthophyll supplementation (115 mg of carotenoids/kg diet/day; 4 weeks) on serum carotenoids, serum concentration of reactive oxygen metabolites (ROMs), serum anti-oxidant capacity (OXY), the degree of oxidative stress (OS; ROMs/OXY £ 1,000), body mass, and skin colour, in rehabilitated captive adult Eurasian kestrels (Falco tinnunculus). The supplementation caused increased levels of serum carotenoids (»90%), ROMs (»82%), OS (»115%) and an immediate loss of body mass (»6.2%), but it did not aVect OXY and tarsi skin hue. The red (»16%) and yellow (»15%) colorimetric components were increased after the Wrst week of supplementation and the eVect persisted during the rest of the experiment. Two months after the end of supplementation, serum carotenoids, OS and ROMs returned to baseline levels, however the body mass did not. Our Wndings suggest that, above a certain physiological threshold, carotenoids can cause detrimental eVects. This is relevant for the tradeoV between expression of sexual signals and the costs of maintaining/producing them.