Abstract
The migratory culling hypothesis posits that infected individuals are less likely to survive long-distance migration due to physiological and behavioral effects, but this lacks empirical evidence. Here, we tested this hypothesis by sampling 357 passerines from 11 species during their autumn migration to wintering grounds in two different areas, i) at a stopover in southern Spain, and ii) in the Canary Islands, where they were drifted and preyed upon by Eleonora's falcons while en route to the southern Sahara. Molecular detection of infections by Plasmodium, Haemoproteus, and Leucocytozoon was conducted on bird samples. A higher prevalence of both Plasmodium and Haemoproteus was observed in birds preyed upon by falcons. While a complete understanding of the mechanistic effects of haemosporidian infections on migration performance needs experimental validation, our approach suggests that infection reduces migration success by increasing mortality due to route deviations and/or predation.