NIOO KNAWKamiel SpoelstraThumbnailWhen people think of pollution, they typically conjure up images of smoggy skies and brown clouds billowing out of factory smokestacks. Not lights. 

Courtesy of NIOO KNAW/Kamiel Spoelstra

When people think of pollution, they typically conjure up images of smoggy skies and brown clouds billowing out of factory smokestacks. However, light pollution defined as the unnatural and/or unnecessary lighting of an environment, usually at night has the potential to be just as harmful. The scale of light pollution can vary from the security light on a back porch that is left on during the night, to the lights on large oil rigs in the ocean. Light pollution can be as little as bridge lighting or advertisements along the highway, but when its looked at from afar, you have a patchy environment that can have a large impact on nature. For bats, artificial lighting can both help or hinder, depending on the type of bat and their lifestyle.

My work was part of a larger project entitled LichtOpNatuur, Light on Nature in Dutch. The project had seven different field sites, and at each site was four sets of street lights, four apiece. Red, white, green, and a control that didnt have a lamp at all. These field sites were natural areas away from sources of artificial light and allowed for a variety of studies. LichtOpNatuur looked into birds, bats, mice, larger mammals, moths, plants, and soil animals, and the five-year long project meant that the long-term effects could be studied. But, back to the bats!

Bat flying in the sky
Natterer’s bat (Myotis nattereri) 
Courtesy of NIOO KNAW/Kamiel Spoelstra

My project in particular was about looking into what effect lights of different colours/spectra have on the hunting preferences of bats, as well as if insects are part of that response do insects gather at these lights (which could then be more food for bats), or do insects have no preference for light?

Bats have been observed hunting around street lights, which can be a risky endeavour what if theyre spotted? What makes it a worthwhile strategy? Furthermore, not all bats like to hunt around light, some avoid it entirely so, does the presence of street lights deter them from hunting there as well?

These are the questions we want to answer.

What we found over two summers was that three groups emerged to have different responses to the light. Slow-flying, light-shy bats (Myotis and Plecotus species) avoided hunting insects in the white and the green lights, while the fast-flying, light-bold bats (Pipistrelle species) showed a preference for the white and green lights compared to the red and control areas. Meanwhile, larger, high-flying species (Nyctalus and Eptesicus species) didnt show a response to spectrum at all, likely because they fly so much higher that street lights arent an issue. Additionally, there was a positive relationship between insect abundance and light spectra more insects at white and green light compared to red light or the dark control.

Bat flying in the sky
Brown big-eared bat (Plecotus auritus) 
Courtesy of NIOO KNAW/Kamiel Spoelstra

So, what we could take away from this is that in areas where light-shy species are at risk of becoming extirpated or muscled-out by other species, reducing the amount of artificial lighting, (or using a red light for security lighting), could prove to be a beneficial conservation tactic. Now, red lights wouldnt work in every single circumstance, but its worth considering in these sorts of situations!

More information can be found at the website of the Netherlands Institute for Ecology, who hosted me and is in charge of the LichtOpNatuur project. Our work was recently published and contains far more information for those interested on the potential impact of artificial nighttime lighting on bats:

Response of bats to light with different spectra: light-shy and agile bat presence is affected by white and green, but not red light
Kamiel Spoelstra, Roy H. A. van Grunsven, Jip J. C. Ramakers, Kim B. Ferguson, Thomas Raap, Maurice Donners, Elmar M. Veenendaal, Marcel E. Visser
Proc. R. Soc. B 2017 284 20170075; DOI: 10.1098/rspb.2017.0075. Published 31 May 2017

About the Author: Kim Ferguson was the recipient of a 2014 BCI research scholarship for her work Bat emergence and return timing with prey interactions at experimentally illuminate sites. Currently, she is working on insect genomics in biocontrol in The Netherlands.