EMERGENT INSECTS AS BOTH PREY AND NEONICOTINOID VECTORS FOR AERIAL INSECTIVORES IN PRAIRIE AGROECOSYSTEMS

Aerially insectivorous birds in North America have declined since the 1980s for reasons that are hypothesized to relate to changes in their insect prey. Agricultural practices have been implicated in these declines, as shifts toward more intensive cultivation alter insect communities and contaminate non-target insects with insecticides. To examine how agricultural intensity affects diet composition and insecticide exposure among aerial insectivores, we evaluated differences in diet via metabarcoding of 309 fecal samples and analysis of seven neonicotinoid insecticides in 389 blood plasma samples in two species, Barn Swallows (Hirundo rustica) and Tree Swallows (Tachycineta bicolor), with known variation in foraging traits. In our study region of Saskatchewan, Canada, both species consumed similar insect taxa dominated by Dipteran families (Tree Swallows: 74% of hits; Barn Swallows: 84%), but Barn Swallow diet was affected by local wetland cover while Tree Swallow diet was shaped by crop cover. At least one insecticide was detected in 30% of Barn Swallow and 25% of Tree Swallow samples. Both species had comparable insecticide exposure, with adult swallows having higher detection frequencies than nestlings and higher concentrations of thiamethoxam, the most prevalent insecticide. Thiamethoxam concentrations were associated with higher crop cover and greater consumption of emergent aquatic insect families. This suggests that in our study system, emergent insects from wetlands are both important prey for swallows and potential vectors of neonicotinoids. Our results underscore the importance of maintaining intact buffered wetlands to protect aquatic habitats from physical and chemical degradation and conserve clean insect prey for aerial insectivores.