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

1, Although a female preference for pairing with brightly plumaged males ha s 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 the se preferences because, by pairing with brightly coloured individuals, fema les can obtain parasite-free and/or more healthy mates. 3, In this paper one of the predictions of this hypothesis is tested, namel y a higher health level in brightly coloured individuals, by analysing the relationships among blood parasites, leucocyte levels and plumage brightnes s in the Girl Bunting, Emberiza cirlus. 4, Two species of blood parasites were detected. Whereas a lower body condi tion was detected in individuals infected by Leucocytozoon cambournaci, no such differences were associated with Plasmodium relictum infections. Infec ted individuals showed higher total leucocyte counts than non-infected indi viduals. 5. Colour intensity of carotenoid derived colorations was negatively correl ated to the relative proportion of lymphocytes and positively correlated to the relative presence of heterophils. Furthermore, the size of yellow feat hered areas was positively correlated with the absolute number of leucocyte s and the relative presence of heterophils. Only some of these relationship s were found for non-carotenoid derived traits. 6, These results suggest that male plumage yellow coloration in the Girl Bu nting is a reliable indicator of health status and supports the hypothesis that females obtain more parasite-free mates if they pair with brightly col oured individuals.