Abstract
Millions of migratory birds are funneled through the Great Lakes Region annually and depend on the shoreline habitats for stopover and refueling. The Great Lakes Region also has a high capacity for offshore wind development. Environmental assessments of a proposed experimental six-turbine array located eight miles offshore from Cleveland, Ohio determined that the impact to migratory birds would be low citing that birds avoid crossing the lake, which contrasts previous individual bird tracking studies showing an estimated 70% of birds crossed Lake Erie after stopping over on the lakeshore. The high crossing rate of some species suggests the potential for increased risk of avian collisions with offshore structures if improperly placed. Collisions with anthropogenic structures such as buildings account for upwards of 988 million annual deaths in the United States. Comparatively, turbines account for lower levels of mortality in the U.S. (679 thousand birds), but these estimates likely underrepresent the total impact due to surveying difficulties and data restrictions for industry reports. Additionally, this number is likely to increase with expansion of wind energy in the United States making now a critical time to close knowledge gaps related to offshore wind impact and to ensure proper siting of turbines that minimizes the risk to migratory birds.
Understanding lake-crossing behavior and shoreline usage of birds in the region is necessary for predicting risk. Using Lake Erie as the focus for this study, I sought to determine the prevalence of lake-crossing behavior for migratory songbirds by tracking the movement of individuals from inland stopover habitats and identifying high use areas along the shoreline. Using automated radio telemetry and the Motus Wildlife Tracking System, I deployed transmitters on 174 birds from a suite of study species including White-throated Sparrow (Zonotrichia albicollis), Swainson’s thrush (Catharus ustulatus), Tennessee Warbler (Leiothlypis peregrina), and Magnolia Warbler (Setophaga magnolia). To more broadly sample migrants moving through the Great Lakes region, I deployed tags across a range of sites concentrating deployments into four main regions: Western Ohio, Central Ohio, Eastern Ohio, and Western Pennsylvania. I collected movement data from 135 birds and found a 31% crossing for birds with known movements. Prevalence of crossing varied spatially between tag deployment regions with more birds from central Ohio having crossed the lake (46% crossing). Variation also existed between focal species with White-throated Sparrow and Swainson’s Thrush having a higher frequency of crossing (29% and 50% respectively) compared to the warbler species tagged. To quantify the variation between species, I calculated the average orientation from the deployment site for each bird, and these results indicated a predominantly northern orientation for White-throated Sparrow and Swainson’s Thrush compared to a predominately northeasterly orientation for Magnolia warblers and Tennessee Warblers. Using the same tracking data, I identified areas of high use along the shoreline of Lake Erie by calculating proportion of use by birds for individual automated receiving stations. I compared proportion of use with proportion of each landcover class from the 30 m North American Land Change Monitoring System within 20 km radius of each station. I developed a set of candidate model to explore patterns of use by birds focusing on the proportion of select landcover classes, Shannon’s Diversity Index (SDI), and forest edge density.
Consistently the models with the most support across species highlighted a negative relationship between use and SDI suggesting higher use in areas of more contiguous landcover. I also found a positive relationship between use and the proportion of urban landcover for Swainson’s Thrush that is supported by a concentration of migrants in and around Cleveland, Ohio. Given the known attraction of artificial light at night for migratory birds, my results suggest that birds are being drawn into urban centers such as Cleveland, Ohio. Evident variation in the prevalence of lake-crossing behavior indicates that certain populations will be more likely to encounter and be at risk for collision with offshore wind turbines. My results suggest that birds moving through central Ohio, particularly White-throated Sparrow and Swainson’s Thrush, will concentrate in Cleveland, Ohio increasing their risk for collision with turbine installations offshore from this urban center. My research demonstrates the need to understand the migratory movements of birds in the region and adds to a growing body of work that can be used to inform siting and mitigation efforts for future offshore wind development within the Great Lakes Region. Throughout each chapter, I have used plural pronouns to acknowledge the coauthors that I intend to publish with, but the intellectual content of each chapter is representative of my own work and research completed for my master’s thesis.
Full text will be available on August 04, 2025.