Light pollution from cities and offshore structures kills and disorients millions of migrating birds annually, representing a significant but preventable source of mortality.
Light-disoriented migrants circle illuminated structures until exhausted, then collide with the structure or become easy prey for predators. During poor weather when migrants are forced low, mortality can involve thousands of birds at single structures in one night. Switching off non-essential lights during peak spring and autumn migration periods is a low-cost, high-impact welfare intervention.