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Plumage coloration deriving from carotenoid and melanin pigments can be a quality signal in birds, and can be under conspecific inspection in social interactions. For example, parasite load and immune system status can be inferred through plumage color intensity, and can influence the choice of sexual partners. Here, we evaluated two plumage ornaments in the Yellow-billed Cardinal [Paroaria capitata (d’Orbigny & Lafresnaye 1837)]: the carotenoid-based coloration of the cap and the melanin-based coloration of the bib. We evaluated whether these ornaments were related to blood parasite burden, immunological status and body condition, and whether they could reveal individual sex and age. Cardinals were mist-netted in a Brazilian wetland, and 12 individuals were infected with malaria parasites. Both carotenoid and melanin colorations were related to age, but only carotenoids reflected immunological status. Adult cardinals presented redder caps and darker bibs in comparison to juveniles, and redder caps were a...

Blood parasites play a fundamental role in the ecology and evolution of passerine birds because they are able to affect the fitness and survival of their hosts. The prevalence of avian malarial parasites among host species can vary from 0 to 100% but the ecological and evolutionary reasons for this variation are not clear. In this study we tested if height or type of nest, body mass or social system, which we believe are variables associated with exposure of hosts to vectors, could explain the variation in the prevalence of blood parasites in a bird community from the Cerrado biome of central Brazil. We found a significant positive correlation between nest-height and prevalence of Haemoproteus, which is consistent with the hypothesis linking prevalence of blood parasites with nesting stratum in North American birds. We also found evidence for increased levels of parasitism by Haemoproteus in neotropical birds that live in groups and breed cooperatively and increased levels of parasitism by Plasmodium in species that nest in cavities or closed cups. We suggest that reproductive and behavioural parameters of hosts may be responsible for their differential exposure to vectors and that these parameters may therefore be able to indicate interspecific variation in the prevalence of blood parasites in other bird communities.