LED-lighting influences urban bat's activities: study

The widespread replacement of conventional bulbs in street lighting by energy-saving LEDs has considerable influence on bats as urban nocturnal hunters, a new study has found.
The study found that opportunistic bats - which hunt on insects attracted by the conventional street light bulbs - lose foraging opportunities.
On the other hand, light sensitive bat species benefit from the widespread replacement of conventional bulbs in street lighting by Light-emitting diodes (LEDs).
LEDs attract fewer insects than conventional mercury-vapour lamps, so that the activity of light-tolerant bat species such as the pipistrelle is lower.
They have a less repellent effect on light-shunning bats, such as many mouse-eared bats - their activity is higher near LED-lights than near mercury-vapour lamps.

This was shown in a recent study by Christian Voigt and Daniel Lewanzik from the Leibniz Institute for Zoo and Wildlife Research (IZW)in Germany.

Conventional high pressure mercury bulbs have a broad spectrum of wavelengths, including those in the ultraviolet (UV) range.
As a consequence, insects are magically attracted to street lighting and indirect light spilling out from houses.
Moths, mosquitoes, beetles and other insects are drawn to the light because of the vacuum cleaner effect. They circle around lamps and become victims of insect-eating predators.
The new LEDs that are used in street lamps do not emit UV light. Thus, insects ignore them and do not buzz around the lamps anymore, researchers said.

Previously, it was well known that opportunistic species tolerate light and hunt even in lit areas in cities at night. Light sensitive species that shun the light mainly hunt in dark parks and forests.
For their study the scientists installed bat recorders on 46 street lamps in six German cities. By recording echolocation calls of hunting bats, bat recorders automatically detect the presence of bats at conventional and LED street lamps.
The results shows the activity of the common pipistrelle diminished by 45 per cent near LED lamps, light sensitive species that usually avoid artificial light increased their activity by a factor of four-and-a-half.

"Bats which are sensitive to light might benefit from the increasing use of LED, but opportunistic species will suffer from it," said Voigt.
The latter will probably have to travel longer distances in order to find sufficient food. The composition of species within local bat assemblages is likely to change in urban environments.
"Both the use of LED lights and the change in activity of bats will have a substantial effect on insect populations, since bats are the top predators for insect populations in the urban environment," Voigt added.