The growth of cities, with their illuminated street lamps and buildings, has led to brighter nights. This has consequences for animals: artificial light illuminates them directly, but it also illuminates the sky, making the stars invisible. However, many animals rely on the stars as a compass for orientation and guidance.
Until now, no scientific study had examined the effects of light pollution on the orientation of animals. For this reason, the University of Würzburg (in Germany), in collaboration with researchers from the University of Lund (in Sweden) has decided to carry out a study.
In the journal Current Biology , the researchers explain that South African dung beetles cannot use their stellar compass under light-polluted skies.
They use the sky to keep their course
When these night beetles encounter a manure pile, they form small balls with the manure and roll them to a safe distance, where they can bury and consume the manure without interference from other beetles.
To avoid competitors who may steal your manure balls, they must quickly move away from the manure pile. They do this by traveling in a straight line, using the starry sky to keep their course.
Under natural conditions, dung beetles disperse far from the manure pile, allowing them to avoid competing with each other. When direct light pollution is available from buildings and street lamps, they move towards bright lights instead of scattering from each other. This can increase competition and waste energy on unnecessary fights for dung balls.
Experiments in the big city and in the country
“We suspect that the flight towards the light of birds and moths may work in a similar way: light pollution could force them to abandon their stellar compass and fly towards bright artificial lights to have any chance of keeping their course,” argued James Foster, researcher belonging to the University of Würzburg.
The experiments were carried out in South Africa, on a rooftop in central Johannesburg, as well as in a rural area of Limpopo province.
“Beetles that saw direct light pollution behaved unnaturally, but remained oriented. But those that saw light-polluted skies but no illuminated buildings were completely disoriented,” Foster stressed.
From this, the scientists concluded that animals that inhabit the interior (that is, between cities and nature) may be more affected by light pollution, since they cannot see stars or street lamps.
