Direct and indirect effects of pesticide exposure on the gut microbiota of a farmland raptor.

Recent studies in humans have shown that certain pesticides could affect the composition and functions of the gut microbiota, an essential modulator of vertebrate physiology, leading to potential dysbiosis. However, this relationship remains largely unknown in wild birds despite the implications of pesticides in the current decline of farmland species. The present study sought to fill this gap by providing data on the association between pesticide concentrations in blood and gut microbiota characteristics in relation to individual traits in a farmland raptor, the Montagu's harrier (Circus pygargus). Results showed that females with higher body condition and higher pesticide load exhibited greater gut bacterial richness and diversity, while the relationship was opposite in males with higher body condition. In terms of taxonomic composition, Proteobacteria emerged as the dominant phylum across all nestlings. Differences in the abundance of specific phyla and genera were observed according to pesticide load, with higher levels of Bacteroidota and Leifsonia, but lower levels of Bulkholderia, in nestlings with higher pesticide concentrations in their blood. This study highlights differences in microbiota and contamination by several pesticides according to the phenotypic characteristics of a wild raptor, and shows that farmland birds can represent relevant biosentinels for assessing the health/proper functioning of ecosystems (One Health approach).