Monitoring of breeding birds provides insight into age-specific interactions with Ixodes ricinus.

Ixodes ricinus (Family Ixodidae), a widespread generalist tick in Europe, feeds on a large number of host species and acts as a major vector for various tick-borne pathogens. Immature stages of I. ricinus are often found feeding on various bird species, but questions remain open regarding ecological interactions between these organisms especially in relation to potential life-stage specific infestation of juvenile birds. Utilizing ongoing monitoring schemes during the breeding season in northern Germany, we studied the occurrence of ticks on birds caught in two independent forest areas during three subsequent seasons (2022-2024) to study relationships between tick infestation and bird-specific traits (i.e., age, body condition). Tick infestation differed significantly between bird species and we observed significant interactions with bird age and body condition. Adult birds showed lower tick burdens in comparison to juvenile conspecifics and tick infestation showed complex interactions with body condition; highlighting multiple mechanisms are most likely influencing our results. Through morphological identification of attached ticks, we could show that I. ricinus larva and nymphs differ in their interactions with bird traits, with only the number of larvae differing with bird age and neither life-stage alone correlating with bird body condition. Taken together, we supported life-stage specific infestation as a potential driver of higher tick burdens in juvenile birds and show how standardized monitoring can provide insight into these interactions.