Intensity of <em>Haemoproteus</em> spp. blood infection differs between wild birds captured using different trapping methods

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Infection with haemoparasites (Haemosporida spp.) is common within wild birds’ populations and has been associated with adverse effects on birds’ fitness and life performance. Existing literature suggests a hypothesis that birds infected with haemosporidians and exhibiting high parasitemia levels may demonstrate reduced activity, potentially leading to their underrepresentation in captures which use stationary traps, such as mist nets. However, there are limited studies demonstrating this phenomenon in wild birds. To study the possible under representation of highly parasitized birds, captured with commonly used stationary mist nets, we compared parasitemia levels of haemosporidian parasites in wild birds captured during spring migration using both actively startling of birds and birds trapped passively into the mist nets. Utilizing cumulative link mixed models, we assessed the influence of trapping methods on parasitemia scores, controlling for factors such as species identity, season progression, and migration distance. Our dataset comprised 1815 individuals of 60 species, including 142 actively captured and 1673 passively captured ones. Although the number of infected individuals was higher in passively caught birds (24 % in active vs 43 % in passive), the study revealed a significant difference between infected birds within two capture methods: despite challenges in balancing sample sizes, and trapping dates, the findings affirm the underestimation of birds having high parasitemia levels with prevalent mist net techniques. We highlight the importance of considering potential biases in trapping methods when studying haemosporidian parasites in avian hosts during migration.