Insights from common buzzard broods on the interaction between infection, watercourse habitats and simuliid blackfly vectors.

Blood parasites of the genus commonly infect many bird species worldwide and are particularly prevalent in birds of prey. As a vector-borne parasitic disease, the infection occurrence overlaps with that of the dominant vectors: blackflies (Diptera, Simuliidae). These blood-sucking insects are dependent on habitats with flowing freshwaters for the development of their larval stages. We investigated the correlation between the proximity to flowing waters and infection probability in common buzzard () broods, as well as the occurrence of adult blackflies directly at the nests. In addition, we investigated the survival of captured simuliids in relation to host infection intensity. In total in 2019, we examined 112 different nests, including 297 common buzzard nestlings, with a prevalence of 56.6% among the nestlings and of 80.3% at brood level. We found no significant association of infection probability with nestling age, the distance to the nearest stream and the sum of the length of streams within a radius of 200 and 1000 m around each nest. The number of blackflies caught around the nest showed a tentative correlation with the probability of infection of the nestlings. Among the subsample of 218 blackfly individuals that survived day one after capture, survival averaged 6.2 days. Our results suggest that transmission is complex and requires consideration of many factors, related to habitat and vector prevalence, especially given their temporal variation.