Since carotenoids can serve as antioxidants and/or immune stimulants, it has been assumed that deposition of carotenoids in feathers or bills can reveal the health status in birds. In order to study the function of carotenoids as signals or immune stimulants, it is necessary to characterise the types of carotenoid molecules in the study species. In this preliminary study, we examined the types of carotenoids in the plasma of four nestlings of the Eurasian magpie (Pica pica) using mass spectrometry. We found that lutein or zeaxanthin is the major carotenoid in the plasma of magpie nestlings. Some minor constituents of carotenoids could be regarded as the metabolized forms of lutein or zeaxanthin. The plasma of magpie nestlings contained both yellow carotenoids such as lutein and zeaxanthin and red carotenoids such as astaxanthin, which may result in the varying degrees of redness in the plasma among the individuals.
