Presence of bald eagles (Haliaeetus leucocephalus) in upland landscapes of the Upper Midwest during winter: implications for wind energy

Over the next 35 years, the United States’ energy produced by wind power is expected to increase dramatically, resulting in construction of many new wind facilities. The Upper Midwest is likely to be a focal area for this... [ view full abstract ]

Over the next 35 years, the United States’ energy produced by wind power is expected to increase dramatically, resulting in construction of many new wind facilities. The Upper Midwest is likely to be a focal area for this development. Over the past five years, the Upper Midwest has experienced the greatest number of bald eagle mortalities at wind facilities. Because bald eagles are strongly associated with waterbodies, research to-date on this species has primarily been limited to riparian corridors. Consequently, upland agricultural landscapes, where wind energy development is occurring, were thought to be benign environments in term of risk to eagles from wind energy. However, a substantial bald eagle presence has since been documented outside of riparian areas; for example, nesting, wintering, and migrating bald eagles have been documented in all counties in Iowa. Significant eagle mortality and increasing eagle use of upland areas have resulted in the need for more information regarding bald eagle biology and movements in non-riparian Midwestern landscapes. In order to guide management and reduce eagle interactions with potentially hazardous anthropogenic structures, we captured and telemetered (GPS-GSM telemetry units) 22 adult and sub-adult eagles in Iowa and Illinois during the winters of 2013-2016. The local movements of these birds were recorded from their capture or arrival on wintering grounds until they departed on spring migration. We collected 328,945 GPS data points as we tracked eagles for an average of 59.1 ± 39.0 (SD) days per bird through the states of Minnesota, Wisconsin, Iowa, Illinois, and Missouri. To understand the environmental correlates of eagle habitat use, we used logistic mixed effects models to compare conditions when eagles were present in upland areas to conditions when eagles were present in riparian areas. We evaluated five models that were comprised of variables describing extreme cold, storm systems, and spring migration conditions, in addition to global and null models. Unpublished results indicated that bald eagles were more likely to be present on upland landscapes during extreme cold events. This suggests that when ice cover restricts foraging on open water, eagles moved into areas where other food sources may have been available and thus may more frequently encounter wind turbines. The relationship between weather and bald eagle foraging behavior may be useful to understand how bald eagles use Midwestern landscapes and thus may help to guide management decisions to aid in the conservation of this iconic species.