Blinded Bats

Blinded Bats

In Australia the idea that bats avoid light would have some orchardists thinking about putting in a few LED floodlights, but in Europe the bats are mostly small insect eaters that do more good than harm. They hide out in whatever gloomy shelter they can find and actively avoid light when they venture out at night. Bats have been associated with old church bell towers (belfries) for so long that people acting crazy are said to have bats in the belfry, or to put it another way, have a few kangaroos loose in the top paddock.

No more bats in the belfries

But the fashion for floodlighting lovely old churches has ruined the bats’ historical haven and driven them from the belfries. A study in Sweden looked at bat colonies in rural churches 25 years apart and discovered that floodlighting was the likely culprit for a decline from 61% of belfries occupied by bats in the eighties to only 38% in 2016. Tellingly, “All abandoned churches had been fitted with flood-lights in the period between the two surveys”. The study goes on to say: “In contrast, in churches that were not lit, all of 13 bat colonies remained after 25+ years between the surveys.” The fact that undisturbed colonies remained “suggests that colonies may persist continuously in the same buildings over very long periods, certainly decades and perhaps centuries, unless the conditions change drastically and force the bats to either move or die.” Lighting a medieval church tower can be unexpectedly disruptive.

Tunnel vision

Trying not to disturb bats led to a clever solution in Germany. A project to turn disused railway tunnels in Wuppertal into part of a recreational trail had to solve an awkward problem. Bats live in the tunnels and are protected under European law. The tunnels needed to be lit for people to find their way, but not interfere with the bats. The lights were mounted halfway down the tunnel wall, leaving the top half of the tunnel completely dark and bat friendly. The directional nature of LEDs and lack of upward spillage helped make the compromise work.

Red light district

Another compromise benefitting bats has been reached in Holland. In a town with the decidedly Dutch name of Nieuwkoop, new LED streetlights are a red colour and according to councillor Guus Elkhuizen, “designed to be friendly to bats”. The ‘light recipe’ is at a wavelength that the bats perceive as darkness, so the creatures of the night can live alongside people in the new housing development.

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