Skyglow forces dung beetles in the city to abandon the Milky Way as their compass

This article was first published by The Conversation.'s Expert voices: Op-Ed and Insights was contributed by the publication.James Foster, Research Fellow at Julius Maximilian University of WrzburgNights are getting brighter all over the world. Light pollution is increasing due to urbanization, new streetlights, security floodlights, and outdoor ornamental lighting.The light floods directly into animals active at night, as well as into the sky. A portion of this light is directed downwards to an earthbound observer. This is called "skyglow", an all-encompassing light that covers the night sky around and in cities, which can obscure any view of the brightest stars.We wanted to see how the night's brightness could affect animals who rely on the sky for their direction. Are their sensitive eyes affected by the bright lights of cities? Do they lose their way if there are no stars in the night sky? To compare the orientation of light-polluted and pristine skies, we used Scarabaeus.satyrus, the well-studied "sky compasse" of the nocturnal beetle Scarabaeus.The study examined the performance of beetles at the University of Witwatersrand, in the inner city of Johannesburg, in regards to dung-rolling. It was done in Limpopo province. Our results confirm that beetles are affected by light pollution, both indirectly through skyglow and directly from bright artificial lights. They become dependent on artificial beacons made of earthbound lights instead of their sky compass.This strategy change comes with a price.Light pollutionThese beetles are found in southern Africa and collect dung from different animals to make a ball. They can remove the dung from their dung pile by rolling the ball away. They are still vulnerable to competition even when they roll their ball away from the dung pile. They will use their internal compass to move in a straight line from the dung pile and leave it as soon as possible.Each beetle takes the dung and rolls it away to an area that is safe for digging into the ground. Then, the beetle climbs onto its ball and does a short pirouette known as the orientation "dance". It looks around for clues that it can use to keep its course. Because it begins each night in unknown territory, the best references are those in sky that remain stable while the beetle keeps the same heading. The primary reference for these beetles on starlit nights is the Milky Way.Continue reading: We still don't know enough about the stargazing beetle, even though it has a small brain.The beetles used artificial light to navigate. They rolled in the same direction, with many beetles moving towards them. They almost always move in opposite directions under natural conditions. They are more likely to roll towards artificial lighting, and may get into fights as they try to steal their dung balls.Artificial light is more likely to lead beetles to concrete and asphalt areas of their immediate environment. They may then find it difficult to dig into the ground to bury their ball.This light pollution could affect more than just dung beetles. Even species that can depend on other compass reference may be affected by the loss of stars. Nocturnal ants use landmarks to make outbound journeys but need their skycompass for homeward travel. Migratory birds use a magnetic compasse to check latitude and magnetic North. However, they also use their sky compass for calibration to their magnetic compass to geographic direction.Animals that depend on the stars for their homes or breeding sites may not be able to locate them in the worst possible scenario. Even with backup systems, starless skies can cause animals to drift off-course, wasting energy, and putting them at risk for predator encounters.Continue reading: Monarch butterflies use magnetism to navigateCity beetle, country beetleTwo sets of ten beetles were collected at the same location and then they were transported to their respective locations.The beetles played their ball in a circle around the arena's edge when the sky was clear. Each beetle was able to be collected at the arena's edge with its ball and placed at the center ten consecutive times without losing its focus. We were able to record ten exit bearings per beetle to determine their accuracy under both clear and cloudy skies.(Image credit to Chris CollingridgeThe experimental conditions were also captured using a fisheye lens pointed towards the sky and a camera. These images were then processed to estimate the compass information that a beetle should have when it does its orientation dance. These images showed that Johannesburg skies were between ten to 100 times brighter then those in rural Limpopo. Skyglow in Johannesburg almost obscured the Milky Way and other star patterns.The beetles from Johannesburg performed as well as those from rural Limpopo, despite the dramatic loss in sky compass references. With remarkable accuracy, they maintained the same heading direction through sequential trials. On closer inspection, it became apparent that they used different strategies to keep their course.Under clear skies, beetles relied on the Milky Way. This was evident by their slight tendency to head towards its brightest regions. The beetles that were exposed to light were more inclined towards brightly lit buildings.Continue reading: Light pollution is leading nocturnal animals astray. The stars and moon are a compass, but they are being trampled by the stars and moon.The same beetles showed a different behavior in our follow-up experiments when they were exposed to one floodlight under clear skies. The floodlight was turned on and they rolled toward each other, but then dispersed when the light was turned off.Our worst fears about light pollution were confirmed. The beetles of Johannesburg lost their sense of direction when bright lights were blocked. They couldn't see the light-polluted skies. People who saw clear skies were comparatively more oriented.Solutions existIt is easy to reduce the exposure of animals to direct and indirect light pollution. If lights are not possible to turn off, they can be shielded from the sky so they don't shine into the environment.More than 130 "International Dark-Sky Places" have been certified by the International Dark-Skies Association. These places are areas where artificial lighting has been modified to reduce skyglow or light trespass. Nearly all of them are located in the northern hemisphere's developed countries.This should be addressed. This gap should be addressed.This article was republished by The Conversation under Creative Commons. You can read the original article.Follow Expert Voices to keep up with the debates and issues. You can also join the conversation on Facebook and Twitter. These views are the author's and may not reflect those of the publisher.