The Bureau of Ocean Energy Management (BOEM) manages renewable energy development on the US Outer Continental Shelf (OCS). The OCS extends from the boundary of each state's jurisdictional waters (generally 3 nautical miles offshore) to the outer boundary of the US Exclusive Economic Zone (~200 nautical miles offshore). In the Atlantic OCS, 1,742,252 acres are presently under lease agreement for development of commercial-scale offshore wind energy facilities (BOEM 2020). The first active offshore wind energy facility in the United States was the Block Island Wind Farm (BIWF), a five 6-MW turbine operation in Rhode Island state waters, where we focused this research project.
BOEM is concerned with the potential impact of offshore wind energy developments on wildlife that occur offshore, including migratory birds. Birds that utilize offshore habitats may be directly affected by collisions with offshore wind turbines or indirectly affected due to altered flight paths or displacement from foraging or resting areas (Drewitt and Langston 2006, Furness et al. 2013, Fox and Petersen 2019). Assessing collision risk is particularly challenging at offshore wind energy facilities (e.g., Erickson et al. 2001, Thaxter et al. 2017), versus land-based wind energy facilities where carcasses can be found on the ground (Smallwood et al. 2020). Therefore, risk assessments in offshore environments are typically based on species specific estimates of exposure to offshore wind turbines. Burger et al. (2011) categorized estimated exposure to offshore wind energy facilities at three nested spatial scales: macroscale (individuals that occur within a geographic region of interest, in this case the Block Island Wind Farm), mesoscale (occurs if individuals are exposed at the macroscale level and fly within the Rotor Swept Zone (RSZ) of wind turbines, 29 to 189 m Above Sea Level [ASL] at Block Island), and microscale (occurs if individuals of the species are exposed at the macro- and mesoscales and fly within the RSZ of wind turbines.).
In this study, we evaluated automated radio telemetry technology and modeling methods to assess bird movements at BIWF. Automated radio telemetry consists of very high frequency (VHF) transmitters ("transmitters" or "tags") that are attached ("tagged") to free-flying animals and emit digitally coded signals on a common radio frequency (i.e. 166.380 MHZ) every 3-10 seconds. Signals are received by automated radio telemetry stations ("receiving stations"), consisting of one or more antennas attached to a structure (e.g. a mast or building) and connected to a data-logger programmed to record data (including tag ID, time stamp, signal strength, and receiving antenna) of all tagged animals flying by. Automated radio telemetry studies are coordinated through the Motus Wildlife Tracking System, a centralized network that collects and disseminates data from all tagged wildlife and receiving stations across the globe (Taylor et al 2017).