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


July 29, 2021 5.12pm

Globally, nights are becoming ever brighter. Increasing urbanisation and the installation of new streetlights, security floodlights and outdoor ornamental lighting all contribute to growing light pollution.

This light floods directly into the eyes of animals that are active at night and also into the skies. There a proportion of it is redirected back downwards towards an earthbound observer. This is known as “skyglow”, an omnipresent sheet of light across the night sky in and around cities that can block all but the very brightest stars from view.

We wanted to understand how this change in night brightness would affect animals that rely on the sky as their compass. Would their sensitive eyes be blinded by bright city lights? Would the disappearance of stars from the night sky cause them to lose their way? So we used the well-studied “sky compass” of the nocturnal dung beetle, Scarabaeus satyrus, to compare orientation under pristine and light polluted skies.

Our study compared the dung-rolling performance of beetles in a rural part of Limpopo province with that of beetles at the University of Witwatersrand in inner city Johannesburg, both in South Africa. Our findings confirm that beetles exposed to light pollution – both directly through the glare of bright artificial lights and indirectly via skyglow that obscures the stars – are forced to change strategy. They abandon their sky compass and rely instead on earthbound artificial lights as beacons.

This change in strategy comes at a cost.


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