Within- and between-brood variations in haemosporidian infections of nestlings reveal complex host-vector-parasite...

Avian blood parasites are vector-transmitted protozoan parasites and common in wild birds. They cause acute and chronic infections at different life stages with potentially detrimental effects on host fitness. Transmission often happens during the nestling period, when biting dipterans have easy access to featherless skin. However, little is known about patterns of infection within and between broods. Therefore, we investigated prevalence of haemosporidians (Leucocytozoon, Plasmodium and Haemoproteus) in Jackdaw (Corvus monedula) nestlings over four non-consecutive years. Prevalence varied by year, averaged at 33.9%, with Leucocytozoon being the most prevalent genus. We found no links between infection and morphometry, nor with sex or hatching date, at the population level. However, at the brood level, among female nestlings, those with shorter tarsi were more likely to be infected than female siblings with longer tarsi. Infection probability was positively correlated with brood size at the brood level, but not at the individual level. Finally, more broods were partially infected than fully infected or uninfected. Thus, the observed patterns in prevalence were manifold, indicating that haemosporidian infections, caused by bites of vectors, are influenced by various factors in this host-vector-parasite system.

The online version contains supplementary material available at 10.1007/s10336-026-02417-1.