Date of Graduation

Summer 2023


Master of Science in Biology



Committee Chair

Jay McEntee


There is a wealth of evidence demonstrating interspecific competition in birds, but often this evidence is localized and may or may not entirely explain range dynamics over large geographic extents. Bewick’s Wrens (Thrymanes bewickii) and House Wrens (Troglodytes aedon) are small passerine birds of the family Troglodytidae. Previous experimental evidence has demonstrated that Bewick’s Wrens suffer from asymmetric interference competition from House Wrens in Kansas, and this evidence has been cited as the likely reason for the historically recent range collapse of the Bewick’s Wren. However, I argue that localized experimental evidence is insufficient to explain abundance trends over large stretches of geographic and temporal space. By making use of several decades of climatic and count data, I applied linear modeling approaches to test the hypothesis that declines in Bewick’s Wren local abundance have corresponded spatiotemporally with increases in House Wren local abundance. I found subtle evidence for effects of competition across some time comparisons but not most time comparisons. I also found geographic variation in the relationships between the abundance trends of these two species, and support for regionally specific competition. These findings suggest that competition with House Wrens has likely been one of the drivers of Bewick’s Wrens’ range declines in the eastern United States over the past several decades. In general, this study demonstrates the utility of statistical modeling approaches in testing hypotheses related to interspecific competition.


interspecific competition, range collapse, geographic variation, climate change, linear modeling, avian ecology

Subject Categories

Ornithology | Other Ecology and Evolutionary Biology | Population Biology


© Zachary H. Vickers

Available for download on Thursday, August 01, 2024

Open Access