Prior to the actual infection experiment, we needed to select a specific parasite strain for experimental infection and constitute donors for both experimental and control groups. We chose Plasmodium relictum cyt b lineage pGRW04, which naturally occurs in our study species . From catches of wild birds in spring 2015, we selected one individual with a natural pGRW04 infection and five non-infected individuals. All birds were kept indoors in isolated vector-proof cages (100 × 60 × 45 cm) supplied with water and food ad libitum (living mealworms plus a mix of boiled eggs and commercial dry food for insectivorous birds (www.versele-laga.com). The pGRW04 infection was multiplied in four recipient birds by sub-inoculating infected blood into the pectoral muscle. We injected approximately 250 µl of a blood mixture (infected blood, 3.7% sodium citrate solution and 0.9% sodium chloride solution in a 4:1:1 mixture) into each recipient's breast muscle within 5 min after blood withdrawal. One non-infected individual was spared and used as a donor for the control group (see below).