Multi-Sensor Logger Tracking Reveals the Threats of Offshore Windfarms to Passerine-Sized Birds

Abstract

Offshore wind energy is a cornerstone of the transition to renewable energy, yet its rapid expansion raises concerns for wildlife. These concerns notably involve small migratory birds whose movements across marine barriers and therefore potential interactions with offshore wind turbines remain poorly understood. Here, we deployed hundreds of miniature multi-sensor loggers on 14 small (12–80 g) bird species from eight families near the N-E Atlantic (Western France and the United Kingdom). We obtained useful data from 13 species and were able to reconstruct their migratory timing, trajectories and flight altitudes with high precision. From 137 sea-crossing flights across the English Channel and the Bay of Biscay, we reveal that most species crossed these maritime barriers almost exclusively at night and routinely at altitudes below 300 m above sea level, overlapping with turbine rotor-swept zones, thereby exposing them to multiple threats, including collision risks and displacement through barrier effects. These findings highlight the critical need to include passerine-sized migrants, often overlooked in biodiversity assessments, in environmental impact studies prior to offshore wind farm installation, as well as in monitoring protocols during the operational phase. Moreover, our study provides a proof-of-concept of the utility of multi-sensor loggers to integrate small bird migration ecology into windfarm planning and sustainable energy transitions.