Seasonal patterns and host traits as drivers of ectoparasite abundance in 3 bat species ( <i>Miniopterus schreibersii</i> , <i>Rhinolophus euryale</i> , and <i>Rhinolophus ferrumequinum</i> ) in the Central Balkans

Abstract Ectoparasite-host interactions are influenced by a complex interplay of factors, including host species, body condition, sex, age, reproductive status, and seasonal variations. These interactions are often complex, varying not only between species but also across different biogeographical regions. This study evaluates how seasonal changes and host characteristics affect ectoparasite abundance on 3 bat species, with ectoparasite abundance as the response variable and seasonality and host traits (sex, age, reproductive status, and body condition) as predictor variables. We examined the total ectoparasite burden and the most prevalent ectoparasite species across 3 bat species from 29 localities in the Central Balkans. The abundance of ectoparasites was influenced by season (Rhinolophus euryale), host sex (R. ferrumequinum), and a combination of season and host sex (Miniopterus schreibersii). Overall, the highest ectoparasite numbers were recorded in spring and summer when bat hosts, particularly females and juveniles, form dense colonies, providing optimal conditions for parasite transmission and reproduction. While there were slight variations between species, ectoparasite reproduction generally synchronized with the host's reproductive cycle. In M. schreibersii, host pregnancy was associated with increased overall ectoparasite abundance, particularly elevating the numbers of Ixodes simplex and Nycteribia schmidlii, whereas lactation specifically led to a significant rise in I. simplex abundance. Additionally, besides season and host sex, host body condition emerged as a significant trait affecting ectoparasite abundance in M. schreibersii and R. euryale. This study highlights key regional and species-specific factors shaping bat ectoparasite communities in the Central Balkans, providing a foundation for future research and conservation.