Light pollution forces a change in dung beetle orientation behavior.

Increasing global light pollution threatens the night-time darkness to which most animals are adapted. Light pollution can have detrimental effects on behavior, including by disrupting the journeys of migratory birds, sand hoppers, and moths. This is particularly concerning, since many night-active species rely on compass information in the sky, including the moon, the skylight polarization pattern, and the stars, to hold their course. Even animals not directly exposed to streetlights and illuminated buildings may still experience indirect light pollution in the form of skyglow, which can extend far beyond urban areas. While some recent research used simulated light pollution to estimate how skyglow may affect orientation behavior, the consequences of authentic light pollution for celestial orientation have so far been neglected. Here, we present the results of behavioral experiments at light-polluted and dark-sky sites paired with photographic measurements of each environment. We find that light pollution obscures natural celestial cues and induces dramatic changes in dung beetle orientation behavior, forcing them to rely on bright earthbound beacons in place of their celestial compass. This change in behavior results in attraction toward artificial lights, thereby increasing inter-individual competition and reducing dispersal efficiency. For the many other species of insect, bird, and mammal that rely on the night sky for orientation and migration, these effects could dramatically hinder their vital night-time journeys.