Intensity of haemosporidian infection of parids positively correlates with proximity to water bodies, but negatively with host survival

In birds, haemosporidian parasites have been found to have direct pathogenic effects on the host with important consequences for their fitness. However, less is known about distribution patterns of parasite vectors, which may significantly affect parasite prevalence, infection intensity and, thus, pathogenicity in hosts. Here, we tested for relationships between infection intensity, survival, predation and distance from water bodies of mixed-species tit flocks. We found that the prevalence of Haemoproteus and Plasmodium infections decreased with increasing distance from forest lakes and bogs outside the bird breeding season. Haemoproteus and Plasmodium parasites were found to be associated with a low survival rate of willow tits (Poecile montanus) in the vicinity of water bodies, while crested tits (Lophophanes cristatus) were affected only by Haemoproteus. Crested tits, a dominant species of parid social groups, had a lower parasite prevalence and they survived better than the subordinate willow tit. This can be explained by the crested tits foraging higher in the pine canopy as parasite vectors supposedly cannot reach hosts in the upper canopy as equally as in lower parts of the canopy. We show that individuals staying in flocks further from the forest water bodies and spending more time foraging in the upper parts of the canopy have higher chances of survival into the next breeding season. This suggests that different forest and canopy areas may differ in terms of parasite risk and associated mortality. Finally, we found that the infection status of parids increases the probability of predation by the pygmy owl (Glaucidium passerinum). We conclude that distance from water bodies and foraging location in the forest canopy may affect the intensity of parasite infection with fitness consequences in wintering parids.