Thanks to human activities, artificial light is increasingly encroaching on nighttime darkness and may affect certain nocturnal species. Some migrating birds are known to become disorientated by red and white light which has led to recommendations to use blue and green light for illumination. However, the effect of this light on migrating bats was not known.
Christian Voigt and colleagues therefore set up green light sources along Latvia’s shoreline at night, exposing bats migrating south to brief periods of artificial green light at a wavelength of 520 nanometers. They recorded and compared the bats’ echolocation calls during lit and unlit periods to assess the impact of the light.
The researchers found that the two most abundant migrating bat species detected, Nathusius’ bats (pictured) and Soprano bats, appeared to be attracted to the green light, with an increase of around 50 percent in calling activity near the light source when the green light was shining.
One possible explanation was that bats were attracted to the light only indirectly, through chasing their insect prey which was itself drawn to the light. However, the light affected the echolocation of bats up to 23 meters away, too far for them to detect insects near the light, and the proportion of calls that were hunting-related ‘feeding buzzes’ did not increase in the presence of green light. Thus, the researchers suggest that these migratory bats are attracted to green light directly and not because of the insects that gather around it.
This research suggests that certain migratory bats are attracted to green light and that it could interfere with their flight paths and even lead to increased collisions. This susceptibility should be an important consideration when designing nighttime illumination as part of a wider bat conservation strategy, the researchers say.
Research Article: Voigt CC, Roeleke M, Marggraf L, Pētersons G, Voigt-Heucke SL (2017) Migratory bats respond to artificial green light with positive phototaxis. PLoS ONE 12(5): e0177748. https://doi.org/10.1371/journal.pone.0177748