Are street lights changing the balance of nature?

We all know light pollution hampers our view of the stars. Not many appreciate what it's doing under our feet, says Tom Davies

You're working on the impact of street lights on animals on the ground. Tell us more.
We know that aerial invertebrates, such as moths, are attracted to street lights and can experience increased rates of mortality as a result of flying into the lights, exhaustion or increased predation by things like bats. What we don't know is if that has a lasting impact on population numbers.

What did you find?
Because aerial invertebrates are quite difficult to study with regard to community composition, we looked at ground dwelling invertebrates, including beetles, spiders and ants, to see if their communities were affected by proximity to street lighting. We found indications that the lights are having a lasting impact on their distribution.

Do such impacts constitute damage?
Damage is a bit of an extreme word. It constitutes a change to the environment, but whether that is a change that matters needs to be investigated.

Broadly, how does such light affect animals?
In a variety of ways. Things that we need to look at in more detail are how artificial light affects things like the circadian rhythm of animals. Light helps regulate many seasonal and daily cycles - when you hibernate, when you come out of hibernation, when you mate, when you come out to hunt.

What about plants?
That is one thing we want to investigate in more detail, in particular we are looking at the impact of artificial lighting on plant phenology, that is their flowering time, times of seed sets, senescence in the autumn - the rate of colour change in leaves, leaf fall and so on. There is the potential that artificial light could be affecting some of those processes.

Do concerns about upward light pollution detract from these issues?
It is a form of pollution we are only beginning to recognise, so anything that gets people talking about it ? including aesthetic reasons such as sky glow that prevents you seeing the stars ? is good.

Why might a new generation of street lights be a worry?
Societies are beginning to experiment with new types of lighting, in particular whiter lighting. If, for example, having whiter street lights allows me to better pick out a pedestrian on the side of the road when I'm driving, then it may allow a ground beetle to pick out its prey against a complex background of colours. We need to know how that affects the ability of animals to carry out tasks.

What could we do if this proves to be harmful?
There is a range of strategies. One is switching the lights off, but I wouldn't want to advocate that as there's a big human element. Dimming the lights, reducing the amount of light scattered into the environment are potential approaches.

Surely this is only going to get worse?
It seems that way. In our paper we quote a figure of a 6 per cent increase in artificial lighting per year globally. Developing nations will see most growth.

Journal reference: Biology Letters, DOI: 10.1098/rsbl.2012.0216

Profile

Tom Davies is a community ecologist at the University of Exeter, UK, working on the Ecolight project to assess the ecological effects of night-time light pollution

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