Blood parasites, leucocytes and plumage brightness in the Cirl Bunting, Emberiza cirlus

1. Although a female preference for pairing with brightly plumaged males has been reported in many species, the reasons for this choice are not fully understood. 2. Parasites have been proposed as playing an important role in shaping these prefer- ences because, by pairing with brightly coloured individuals, females can obtain para- site-free and/or more healthy mates. 3. In this paper one of the predictions of this hypothesis is tested, namely a higher health level in brightly coloured individuals, by analysing the relationships among blood parasites, leucocyte levels and plumage brightness in the Cirl Bunting, Emberiza cirlus. 4. Two species of blood parasites were detected. Whereas a lower body condition was detected in individuals infected by Leucocytozoon cambournaci, no such differences were associated with Plasmodium relictum infections. Infected individuals showed higher total leucocyte counts than non-infected individuals. 5. Colour intensity of carotenoid derived colorations was negatively correlated to the relative proportion of lymphocytes and positively correlated to the relative presence of heterophils. Furthermore, the size of yellow feathered areas was positively correlated with the absolute number of leucocytes and the relative presence of heterophils. Only some of these relationships were found for non-carotenoid derived traits. 6. These results suggest that male plumage yellow coloration in the Cirl Bunting is a reliable indicator of health status and supports the hypothesis that females obtain more parasite-free mates if they pair with brightly coloured individualsPeer reviewe