A wind turbine in Europe or North America kills, on average, 2.3 birds and 2.9 bats each year, according to a 2012 report by the Netherlands Institute of Ecology, writes Richard Collins.
Migrants are particularly vulnerable. Scientists at the University of Exeter, using sniffer dogs to locate carcasses at UK wind-farms, found that bat “casualty rates varied from 1 to 64 per month across 29 sites”. The overall toll was 194. Common and soprano pipistrelles were the main victims.
Bats fly into rotors. Even if a bat isn’t struck, the sudden drop in air pressure passing between the slashing blades, can burst its lungs. The echo-locating princes-of-darkness aren’t ‘blind as bats’; they can see. Studies at Wolf Ridge Wind Farm in Texas suggested that bats mistake turbines for trees, sources of insect food and shelter.
Artificial light tends to be avoided, but clusters of insects swarming around streetlamps can attract these aerial-feeding carnivores. Are they also drawn to the aircraft warning lights mounted on turbine towers? These are usually red. Is the colour significant?
“Red light has no effect on bat activity,” claimed a Netherlands Institute press release in May 2017.
Artificial light at night can have a disruptive effect on bats, but not if the light is red. Wind turbines should continue to be fitted with synchronised flashing red aviation lights, as this form of lighting does not appear to be one of the potential causes of bat fatalities
A study just published challenges these conclusions. According to the Leibniz Institute in Berlin, “the use of red light signals could have fatal consequences for them (bats) as this appears to attract them to operating wind turbines”. This conclusion comes from experiments carried out on the Baltic coast, along which huge numbers of bats migrate in late summer.
Latvia’s Pape Nature Reserve, with its large coastal lagoon, attracts bats. The Berlin researchers attached coloured lights to a pole there and positioned bat detectors near it. Lights of various colours were switched on for ten-minute periods, interspersed with intervals of darkness. The numbers of bats approaching the pole were estimated from echo-location calls.
No increased activity was detected when white lights were on, compared to the situation during periods of darkness. However, when red lights were deployed, bat numbers increased. Common and Nathusius’s pipistrelles, both migrant species, were the main ones recorded.
What can be done to minimise bat mortality at windfarms?
Clearly, it’s important to identify migration routes and avoid locating farms on them. Turbines could be turned off at night during peak times of bat activity and bird migration, their operators being compensated for doing so. Alternatively, warning lights might remain off, until activated automatically when an approaching aircraft is detected by radar. Do the lights have to be red? The Baltic research might suggest that white ones may be preferable.
We have common and soprano pipistrelles in Ireland, although our ones don’t appear to migrate. One Nathusius casualty was recorded in the Exeter survey. Europe’s most migratory species, a Nathusius tagged in Russia, travelled 1,600km. A Latvian and two Lithuanian migrants have turned up in Britain and a UK-tagged individual visited the Netherlands. The presence of Nathusius in Ireland was confirmed in 1997.
CC Voigt et al. Migratory bats are attracted by red light but not by warm-white light: Implications for the protection of nocturnal migrants. Leibniz Institute for Zoo and Wildlife Research.