Can Artificial Light Deter Nocturnal Predators at Common Tern Nesting Sites? An Experimental Study

Nocturnal predation by Black-crowned Night Herons (Nycticorax nycticorax) is a major cause of nest failure for Common Terns (Sterna hirundo) and other waterbirds, but few management techniques exist to reduce it. In 2021, an experiment investigated whether artificial lights reduced nocturnal activity of night herons at a tern colony and decreased nest predation. An Experimental Area, with sixteen low-intensity solar garden lights, was established adjacent to an unlighted Control. Tern and heron behaviors were monitored by trail cameras taking time-lapse and motion-sensitive photos and videos; predation was recorded during site visits. Night herons were detected six times less frequently in the Experimental Area than in the Control and fewer tern chicks and eggs were predated in the Experimental Area. Common Terns attended their nests 25% longer in the Experimental Area, but no obvious behavioral changes could be detected. Night heron activity and predation intensity were therefore lower in the presence of artificial lights. Thus, it appears that artificial lighting can modulate night heron hunting activity in tern colonies by changing illumination intensity. Artificial lights have promise as a management tool to reduce night heron predation at tern colonies.