Do seabirds dream of artificial lights? Understanding light preferences of Procellariiformes
Seabirds, and particularly fledglings of burrow-nesting species, are greatly impacted by light pollution. During their inaugural flights from colony to sea, fledglings become grounded after encountering artificial light. Such groundings, or fallout events, affect many fledglings each year. To mitigate this light induced mortality, rescue programs have been implemented for decades in many locations worldwide. Despite the notoriety of fallouts, the contributing behavioural and biological factors remain mostly unknown. How do the mechanisms of light attraction and light avoidance interact or how do they manifest in different groups (e.g., age, personality, populations), or light pollution levels, remain open questions. We tested behavioural preferences of Corys shearwater Calonectris borealis fledglings, rescued after being grounded in urban areas, and of breeding adults, for contrasting light sources. Fledglings and adults were exposed to one of the three treatments in an experimental y-maze set-up: white light versus no-light, blue versus red light, and a control with no-light on each arm of the y-maze. Both age groups have shown preferences for the no-light arms and the red light arm. The preference for longer wavelengths and darker environments, along with slower responses by fledglings, suggest that close range light pollution appears to cause disorientation in seabirds. Our study helps to clarify the behavioural components of fallouts and provides further evidence on the disruptive effects of nocturnal artificial light on sensitive species.