Context-dependent prevalence of neonicotinoid insecticides in a predatory songbird, the loggerhead shrike (Lanius ludovicianus)

Neonicotinoids are a class of widely used insecticides typically considered safe for non-target organisms, but numerous studies have documented adverse effects across diverse taxa. Despite this, documentation of neonicotinoid residues in vertebrates and their subsequent impacts, especially at higher trophic levels, remains limited. We investigated the prevalence and concentration of neonicotinoid residues in the blood of loggerhead shrikes (Lanius ludovicianus), declining predatory songbirds, occupying agricultural and non-agricultural regions. We also evaluated associations between neonicotinoid presence and measures of health and fitness, including body condition, survival, and reproductive success, as well as demographic and habitat variables. In initial sampling, neonicotinoids were detected in 24 of 30 (80%) breeding shrikes across agricultural and non-agricultural regions. Imidacloprid (0.6-7.9 ng/mL) and clothianidin (0.5-0.9 ng/mL) were detected in the agricultural region, while imidacloprid (1.6-7.0 ng/mL) was also detected in the non-agricultural region. Despite the high prevalence, we did not detect associations between neonicotinoid presence and the measured health metrics. However, patterns of neonicotinoid exposure varied among demographic and finer-scale habitat factors, with greater neonicotinoid presence detected in juveniles and in shrikes breeding in areas with a greater proportion of rice fields rather than cotton or corn. Differences in analytical sensitivity and associated small sample sizes may have limited our ability to evaluate these patterns and highlight the need for further sampling. Overall, our findings contribute to evidence of widespread neonicotinoid presence in vertebrates and demonstrate context-dependent exposure patterns that vary among compounds, demographic groups, and habitats.