Blood parasites, reproduction and sexual selection in the red-backed shrike (Lanius collurio)

We investigated the occurrence of blood parasites on the red-backed shrike Lanius collurio during a three-year study in southern Czech Republic. Selected traits of shrike body morphology, male plumage and reproduction were studied with respect to the presence and intensity of haematozoan infection in blood samples collected from 172 breeding adults. Haemoproteus lanii was found to be the most common parasite (72.7%), the prevalence of other parasites (i.e., haemoproteids Plasmodium sp. (cf. relictum) and Leucocytozoon sp., kinetoplastid Trypanosoma sp. and microfilariae Aproctella stoddardi) being markedly lower. Incidence of parasitemia did not differ between sexes in any of the parasite species considered. However, females infected by Haemoproteus lanii initiated egg-laying later in the season than uninfected females. Among males, infected individuals had significantly longer wings and larger melanin-based tail colour patterns (a secondary sexual trait) than uninfected individuals. Moreover, mating was assortative with respect to infection status.