Date of Award
Open Access Thesis
Master of Science (MS)
David R. Brown
Valerie E. Peters
Luke E. Dodd
In the 1960’s the invasive Hemlock Woolly Adelgid (Adelges tsugae [hereafter, HWA]) began to spread west across the hemlock stands of the Eastern U.S. killing a significant number of Eastern Hemlock (Tsuga canadensis). While chemical treatments, primarily with the active ingredient imidacloprid, have been implemented, their effects on hemlock dependent avian species are largely unknown. A 2009 study, which took place as HWA was beginning to invade Kentucky, identified six indicator species that were positively and negatively correlated with eastern hemlock stands throughout the Appalachian Mountain region of Kentucky. Our study repeated bird and vegetation surveys at the same 65 sites in 2018 (nine years later), to conduct a before-after-control-impact test of how the six avian indicator species and hemlock health have responded to chemical treatments. To better understand the mechanisms linking hemlock decline with changes in the bird community, the following three values were quantified: (1) the proportion of dead to live hemlock trees, (2) hemlock decline using an index based on canopy vigor, and (3) the importance value of hemlocks between years in treated vs. control sites. Generalized linear mixed models were used to ask if indicator bird species, abundances were related to percent dead hemlock, hemlock importance value, the hemlock decline index, chemical treatment, and year. Management area was included in all models as a random effect. Canonical Correspondence Analysis (CCA) was used to determine if the entire avian community had changed between years. We found an 11% increase in the percent dead hemlock across sites since 2009, regardless of chemical treatment. While hemlock canopies had higher vigor in treated sites, there was no significant difference in the hemlock decline index between treated and untreated sites. None of the six focal bird species showed a significant population response to chemical treatments (based on the interaction of treatment and year). The Black-throated Green Warbler (Setophaga virens) significantly declined between years across both treated and untreated sites. Although Acadian Flycatcher (Empidonax virescens) and Blue-headed vireo (Vireo solitarius) did not decline significantly over time, I found species association with hemlock and year to have a significant impact on the variation in total abundance of focal species. Red-eyed Vireo (Vireo olivaceus) and White-breasted Nuthatch (Sitta carolinensis) did not show a significant increase between years. However, Eastern Wood-Pewee (Contopus virens) significantly increased between 2009 and 2018. Our results suggest that while treatments have a positive effect on individual hemlocks, this effect is not carried over to the hemlock dependent avian species. This could be due to limitations in the effectiveness, as well as delays in implementation of chemical treatments within our sites. In fact, we may not see a significant decline in positive hemlock associates until some threshold of dead hemlock or poor hemlock health is met. This study suggests that more frequent and widespread treatment is needed to slow the decline of Kentucky’s hemlock stands and protect hemlock-dependent avian species.
Copyright 2020 Natalie Sweeting
Sweeting, Natalie, "Abundance Of Songbirds In Eastern Hemlock Stands Following Chemical Treatment For Hemlock Woolly Adelgid" (2020). Online Theses and Dissertations. 676.