PARASITES, PLUMAGE COLORATION AND REPRODUCTIVE SUCCESS IN THE YELLOWHAMMER, EMBERIZA-CITRINELLA

The prevalence and intensity of haematozoan parasites, with special em phasis on Haemoproteus coatneyi, was studied in relation to male pluma ge coloration, and reproductive success in a population of yellowhamme rs (Emberiza citrinella). Parasite prevalence and intensity were found to vary with time in season, emphasising the need to take samples dur ing times of developed infection. Males were found with a peak intensi ty during the early breeding period and females slightly later, during the nestling period. The hypothesis of parasite-mediated sexual selec tion, according to which bright plumages have evolved in relation to d egree of parasite infection, was tested. Male colour was found to reli ably reveal the intensity of parasites during the breeding period. Mal es with high parasite intensity produced fewer fledglings. In spite of the negative correlation between parasite load and colour, males with more colour did not produce more offspring. No cost of parasites was found in females, and pairing was not assortative with respect to para site infection. However, contrary to the hypothesis, no relationship b etween male colour and number of fledglings was found. Conclusively, s ome support was found for the hypothesis of parasite-mediated sexual s election, i.e. bright male plumages in the yellowhammer may thus have evolved or is maintained as a signal of level of parasite infection si nce a reduced reproductive success may be a cost imposed by high paras ite load.