Experimental Evidence That Blood Parasite Infection Affects Incubation Patterns in a Cavity‐Nesting Songbird

Avian chronic hemoparasite infections occur commonly in wild birds, causing adverse effects on host fitness and breeding success. However, the potential impact of such infections on the incubation behavior has been scarcely experimentally studied. We reduced the infection of hemoparasites in wild-breeding female pied flycatchers (Ficedula hypoleuca) through medication with primaquine to test the possible effects on incubation patterns compared with non-medicated control females. As predicted, medicated females significantly reduced their parasite infection compared to control females. This had a direct significant effect on the female behavior, as medicated females were able to have longer incubation sessions, while control females reduced the time devoted to each incubation session. In addition, females from both treatment groups spent less time incubating as incubation progressed, with control females showing a greater reduction. In contrast, the average length of recess sessions did not vary across treatment groups. Moreover, incubation sessions were more frequently interrupted when clutches were smaller. However, these changes had no apparent effects on immediate fitness. To our knowledge, this is the first study showing changes in individual incubation patterns in response to parasites in a wild-bird population, adding to previous studies showing that blood parasites have detrimental effects on bird reproductive success.