Streetlights' latest foe: Bats

Modern streetlighting has faced plenty of opposition from people worried about its negative impact on human health and safety. Now, it's meeting its latest foe: Bats.

Speaking on behalf of the flying mammals, Dr. Fiona Mathews, from the University of Exeter in England has called for a reduction in streetlighting and outdoor home lighting, as reported by the Western Morning News.

Mathews, a mammalian biolgist, has just published research reaffirming what a lot of us already knew: bats don't like light, and light, in fact, can harm them. According to the story, many people wrongly believe that bats do like light.

'We already knew that lighting was bad news for rare species such as horseshoe bats,' Mathews said. 'Now we have demonstrated that, for the common species of vital importance to our ecosystem, lighting is not helpful. Over recent decades, the number of streetlights, and the brightness of lighting, has grown enormously. We also use increasingly powerful lights to illuminate outdoor areas around our homes. We urgently need to reverse this trend.'

Mathews' research, conducted in partnership with Bat Conservation Ireland, singled out Leisler's bat as one species that bucks the trend and likes light. Leisler's is rare in Britain but common in Ireland.

But for most bats lights can disorient them and their vision (contrary to popular belief, bats can see).

“When we walk out of a lit house into the dark, it takes a while for our eyes to adapt to the darkness,' said Mathews. 'The same is true in bats – they are dazzled by bright light and it takes time for their eyes to re-adjust. This could affect their ability to navigate. In addition, it seems that their ability to hunt insects is reduced in the light.

This is not the first time that bats have recently stared daggers at an outdoor lighting scheme. When the German city of Wuppertal wanted to light up a disused railway tunnel as part of a new cycling and recration trail, it mounted downward pointing LED light lights well below the tunnel ceiling in order to leave a stretch of darkness where the bats – who were there first – could continue to thrive. 

Meanwhile, streetlighting opposition continues from the human ranks. Some people, like UK campaigner Simon Nicholas, worry that the blue spectrum common in LED lighting can disrupt circadian rhythms and can even contribute to cancer. In response to pressure, Wigan Borough recently implemented an LED streetlighting scheme that has a warmer colour temperature than the cold blue it had originally planned.

And residents in many towns have complained that new LED streetlights cast only a narrow beam of light and thus leave swaths of walkways and public areas in crime-inviting darkness. Wait – maybe that's good for the bats?!

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Illustration of horseshoe bat is from Nicolas Primola via Shutterstock

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