Quantitative PCR Analysis of Haemosporidian Infection Intensity in a Temperate Bird Community

Avian haemosporidians are vector-borne parasites with complex transmission dynamics influenced by host ecology and environmental factors. Both prevalence and parasitemia are key measures in host-parasite studies. While prevalence reflects the proportion of infected individuals in a population, parasitemia provides insights into the intensity of infection within hosts, offering a different but complementary perspective. In this study, we used quantitative PCR (qPCR) to investigate seasonal and interannual variation in haemosporidian infection intensity among 266 individuals from six bird species in a temperate woodland in Slovakia over 3 years (2017-2019). We focused on the four most abundant taxonomic groups: Erithacus rubecula, Sylvia atricapilla, two parid species (Parus major, Cyanistes caeruleus), and two turdid species (Turdus merula, T. philomelos). Our results revealed distinct, taxon-specific seasonal trajectories. Turdid species showed similar unimodal summer peaks, whereas parids lacked early spring infections and exhibited a steady decline from summer to autumn. E. rubecula demonstrated a gradual increase across the season, while S. atricapilla showed a bimodal pattern with peaks in late spring and early autumn. Spring intensities were highest in 2017-2018, likely due to relapse or new infections, and lowest in 2019, coinciding with warmer and wetter conditions. These findings highlight how seasonal variation in environmental conditions, such as temperature and precipitation, interacts with host life history to shape infection intensity patterns. Our study emphasizes the importance of integrating ecological context with molecular tools to better understand haemosporidian dynamics in wild bird populations.