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Floodlighting is driving bats from some of their last strongholds in rural churches, according to the first detailed before-and-after study.

The towers, attics and belfries of rural churches are ideal roosting spots for a range of bats. But the animals require darkness so they can avoid predators when they venture out on hunting expeditions. So the growing popularity of floodlighting even remote rural churches is threatening their survival, says of Lund University in Sweden.

In a unique study last summer, he revisited 61 rural churches in south-west Sweden that he had originally surveyed for their populations of brown long-eared bats in the 1980s. Back then, none of the churches had been floodlit; but now many were often lit up on all four sides.

His findings were stark. All 14 churches that had remained unlit since the 1980s still had their bats. But of those now partially lit, half had lost their bats. And there were no confirmed colonies in a single church fully lit for most of the night, concluded Rydell.

A typical example was a small wooden church in Varnum, 60 kilometres east of Gothenburg. “There were bats in the tower in 1983, but no trace in 2016,” says Rydell. In the meantime, “four strong floodlights were installed, one from each direction”.

The study only covered long-eared bats, but Rydell says other slow-flying species such as mouse-eared and horseshoe bats will probably show the same pattern.

Age of “enlightenment”

It was not all bad news, however. Near to Varnum is Brunn church, which has a high narrow tower ideal for bats. Here, says Rydell, bats have survived the installation of three “sharp and aggressive floodlights” in the 1990s, because the fourth side of the tower remains dark.

“We counted 68 bats leaving the attic in the evening. Every one emerged from a narrow dark corridor at the eastern end of the church near to a big oak tree that almost reached the church wall,” he says. Without that dark escape route “they would probably have little chance against the tawny owls and kestrels”.

He concludes that the minimum requirement seems to be to leave one side of the church unlit, preferably the part that is nearest to surrounding protective tree canopies.

“Artificial lighting is a threat to practically all bat species,” said at the University of Naples.

Such floodlighting appears to contravene European conservation law. The Habitats Directive protects all bat species and makes it an offence to disturb them. Yet even in law-abiding Sweden, the disturbance caused by lights seems to be widely ignored.  It’s not malice, says Rydell, just ignorance.

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