Würzburg. When the light of brightly lit cities “obscures” the night sky, we speak of light pollution. This effect makes it impossible for nocturnal beetles to orientate themselves in the starry sky, as an international research team with experts from the University of Würzburg found out. This should also apply to nocturnal birds and moths.
The growth of cities with their street lamps and illuminated buildings makes the nights brighter. This has consequences for animals: the artificial light illuminates them directly, but also illuminates the sky, making the stars invisible. But many animals rely on the stars as a compass for orientation.
So far, there has been no scientific study that investigated the effects of light pollution on the orientation of animals using a star compass. A research team led by Dr. James Foster from the Biozentrum of the University of Würzburg, together with the University of Lund in Sweden and the University of Witwatersrand in South Africa, has now changed that.
In the journal Current Biology, the team shows that South African dung beetles (Scarabaeus satyrus) are unable to use their star compass under light-polluted skies.
Get away from the dung heap quickly
When these nocturnal beetles find a pile of dung, they form small balls out of the dung and roll them to a safe distance. There they can bury and eat the dung without being disturbed by other beetles.
To avoid hungry competitors who might steal their dung balls, they have to run away from the dung heap quickly and purposefully. They move in a straight line and use the starry sky to keep their course. In natural conditions, the dung beetles disperse away from the dung heap so that they do not compete with each other. However, when there is direct light pollution from buildings and streetlights, they move toward the bright lights rather than moving away from each other. This can increase competition and waste energy in unnecessary fights for the dung balls. “We suspect that this ‘flight into the light’ also occurs in birds and moths: The light pollution could force them to give up their star compass and fly towards bright artificial lights in order to have any chance of staying on course,” says Dr . James Foster from the Biozentrum of the University of Würzburg.
The experiments were carried out in South Africa, on a rooftop in the middle of Johannesburg as well as in a rural area in Limpopo Province. “Beetles that saw direct light pollution behaved unnaturally, but were still able to orientate themselves in the terrain. But those who could only see a light-polluted sky and no brightly lit buildings were completely disoriented, ”says Foster.
From this, the scientists conclude that animals that inhabit the hinterland between cities and the wilderness may be most affected by light pollution – because they cannot see stars or street lights. Read in the publication: “Light pollution forces a change in dung beetle orientation behavior, James J. Foster, Claudia Tocco, Jochen Smolka, Lana Khaldy, Emily Baird, Marcus J. Byrne, Dan-Eric Nilsson, Marie Dacke, Current Biology, July 29, 2021, DOI: 10.1016 / j.cub.2021.06.038 “