Fruit parasitism and abundance of a non-native insect pest affects abundances of some songbirds

Non-native insect pests can have significant effects on forest ecosystems. Forest fruit-targeting non-native insect pests may cause extensive damage to fruits, reducing food for fruit-tracking wildlife. Parasitism of forest fruits by spotted wing Drosophila ( Drosophila suzukii , SWD) may put it in competition for fruits with fruit-consuming forest songbirds during their post-breeding and migration seasons. Our objective was to identify factors, primarily SWD abundance and fruit parasitism, influencing frugivorous and non-frugivorous bird relative abundance and species richness in regenerating timber harvests invaded by SWD in western Pennsylvania during the post-breeding season and fall migration in 2019 and 2020. Eastern towhee ( Pipilo erythrophthalmus ) relative abundance correlated negatively with SWD counts, while hooded warbler ( Setophaga citrina ) relative abundance correlated negatively with fruit parasitism. Most bird relative abundances correlated to vegetation structure or date, not SWD variables. Eastern towhee possibly viewed fly-covered fruits as less desirable for consumption or were deterred by SWD swarms disturbed while foraging on or near the ground. Based on modeling results of hooded warbler, SWD activity may have shifted arthropod community composition and impacted some arthropod-consuming birds via trophic cascading effects: parasitism-induced fruit drop driving arthropod prey from foliage, deterring some foliage-gleaning birds (hooded warbler). Frugivorous birds either did not alter fruit consumption or masked relationships to SWD likely by altering diet and foraging behavior, demonstrating an apparent resilience to invasion complemented by the importance of date. Investigating arthropod communities and consumption of fruits in habitats invaded by SWD are critical next steps to understanding ecological effects of SWD.