Spotted wing drosophila (Drosophila suzukii) is a recently introduced invasive fruit fly that parasitizes fruits of many plant species in the United States. While its impacts in invaded forests are unknown, parasitism could reduce soft mast food for wildlife, including migratory songbirds. This may reduce food availability for birds in valuable early successional forest habitat before and during fall migration, when energetic demands are greatest. Our objective is to identify factors influencing frugivore and non-frugivore bird abundances in regenerating timber harvests invaded by spotted wing drosophila during the postbreeding season and migration.
From July through October of 2019 we mist-netted birds across twelve timber harvests at Allegheny National Forest in northwestern Pennsylvania. At each net we conducted fruit surveys, fly trapping, and vegetation surveys to quantify factors influencing bird abundances. We also collected a small sample of fruits at each mist net and observed for emergence of D. suzukii, for a measure of infestation rates of fruit.
Results/Conclusions
In 2019, we banded 1,733 birds from 67 species and collected 350 fly traps and 136 fruit samples to quantify extent of fruit infestation. Between 18 July and 22 August, 39.1% of birds were frugivores. Between 22 August and 25 September, 25.0% were frugivores. Mean (±SE) fly counts at each net were below 50 until August 15 (140.4±15.4) and increased by 763% from 25 (240.6±54.9) -28 (1836±472) August. Most fruit samples (66.9%) contained adult flies.
These data suggest significant fly activity beginning in August, with potential implications for frugivorous songbird habitat use during the critical postbreeding season. We will conduct further surveys and analyses in 2020 to understand how D. suzukii influences songbird abundances against other quantified factors.