Eastern purple martins (Progne subis subis) rely exclusively on human-provided nesting structures, where landlords often apply the carbamateinsecticide, carbaryl, to control haematophagous mites. While effective against pests, the unintended physiological consequences of carbaryl exposure on developing nestlings remain poorly understood. This study investigated the impacts of carbaryl on the gut microbiome and morphometric condition of wild nestlings across three field seasons. Using 16S rRNA DNA metabarcoding, I analyzed 134 fecal samples to compare microbial diversity and composition. While alpha diversity (richness and evenness) did not differ significantly between groups, beta diversity analyses revealed significant shifts in microbial community composition associated with carbaryl exposure. Notably, treated birds exhibited a 12.3% increase in the relative abundance of opportunistic pathogens within the family Mycoplasmoidaceae. Conversely, linear mixed-effects models showed no significant differences in body mass, wing chord, or head-bill length between treatment groups. These results indicate that carbaryl exposure induces sublethal shifts in microbial community structure that do not appear to obstruct short-term structural growth or body condition at 19 days post-hatch. This research highlights the importance of evaluating the broader biological impacts of insecticide use in wildlife management.
Stephanie A. Gaspar
Dr. Robert Fitak, Advisor
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