New BioClock research: the benefits of light dimming and darkness in cities for bats and insects

It attracted a quite some attention from local residents when BioClock researchers  Hannah Broeckx and Sander Buddendorf came to hang their measuring equipment on lampposts in The Hague and Rotterdam. They were conducting research into the effects of dimmed versus bright artificial light at night on urban pipistrelle bats and their prey: flying insects.

We are all familiar with the image: a street lamp with a swarm of flying insects captivated by the light. This behavior is very harmful to insects. They become exhausted, are burned by the lamp and are easy prey for predators, such as certain bat species. However, these bats are also victims of the bright lights. The light attracts so many insects that competition in the dark may increase.

So, the question is: what can we do about this? In a recently published study, BioClock researchers Hannah Broeckx and Sander Buddendorf investigated whether dimming street lighting could offer a solution.

Measuring insect and bat activity

They attached their measuring equipment to a dark control pole and several lampposts that alternated between normal and dimmed light each night. Insect activity was measured by a camera focused on a sticky plastic A4 sheet, and bats through a microphone that can record their echolocation. This allowed them to determine exactly how many insects were attracted and how active the bats were under the different lighting conditions.

Key findings

It turns out that dimmed streetlights attract significantly fewer flying insects. However, both bright and dimmed light caused insect activity throughout the night to differ from the dark control. The researchers also observed that pipistrelle bats prefer to hunt in the dark rather than under dimmed lanterns, and therefore do not blindly follow insects towards the light.

Although dimming cannot replace natural darkness, the researchers believe it is a simple and useful measure for preserving urban biodiversity. However, preserving dark areas remains crucial!

Read the full study here.