M49EXB Common toad (Bufo bufo) on Brandon Hill with Cabot Tower in the background, Bristol, UK. March
Artificial light disrupts toads’ night-time breeding ritual, reducing numbers © Alamy

Artificial light is the latest bête noire of gardens, increasingly being seen as a threat to wildlife, from insects and amphibians to birds and mammals.

Even sceptical gardeners, those who consider agrochemical corporation Monsanto to be the equivalent of Saint Fiacre, the patron saint of gardens, might be encouraged to think twice about installing artificial light when they consider that common garden slugs thrive under it, according to some research.

One glimmer of hope is that certain types of artificial light are far less disruptive to wildlife than others, and technological tools that can help identify them are now in development.

The sight of moths and other insects clustered around artificial lights is commonplace, and so too is the debris of dead insects at their base. This body banquet may be one of the reasons that slugs seem to thrive in illuminated areas, according to Roy van Grunsven, a Dutch scientist.

His study, carried out in Germany over four years, revealed that the common garden slug, Arionidae, does well in artificial light at night: surprising, given that they are mainly nocturnal animals.

Van Grunsven has been looking at the effect of artificial light on wildlife for about 10 years. “We know that many species depend on darkness,” he says. “Many species are active at night — some only do certain things when it is dark.”

Moths, for example, feed less if it is lighter at night, and female moths produce fewer pheromones, attracting fewer males and mating less. Glow-worms struggle with any light that competes with their own. And artificial light affects birds in a number of ways, says van Grunsven.

“For glow-worms light is essential for communications, and if it isn’t dark this communication breaks down. Birds that have been exposed to artificial light can suffer sleep deprivation and stress,” he says.

Glow-worms need light for communications, and if it isn’t dark this communication breaks down
Glow-worms need light for communications, and if it isn’t dark this communication breaks down © Alamy

“Birds also use light/dark rhythms for timing. Artificial light causes some birds to sing earlier in the morning, while other birds wake earlier in town than the country. It may depend on species,” says van Grunsven. “Also, annual timing is affected; in illuminated places birds can lay eggs earlier in the year. This sounds harmless, but if they have young too early there is not enough food.”

Bats normally emerge at dusk to feed on insects. Artificial light obscures dusk, so bats miss their feeding times. Amphibians such as frogs and toads croak at night-time as part of their breeding ritual but artificial light disrupts this, and so reduces populations.

Artificial light can cause bats to miss feeding time, since they normally feed at dusk
Artificial light can cause bats to miss feeding time, since they normally feed at dusk © Alamy

In some respects, it’s surprising it has taken us so long to wake up to the impact of light pollution on wildlife. In the early 20th century, dead birds around the Eddystone lighthouse in Devon alerted naturalists to the problems some animals have with artificial light.

In 1993, Toronto launched its Fatal Light Awareness Programme by having many of its tall buildings switch off their lights at night, saving up to an estimated 9m birds a year.

Artificial light does not only cause birds to crash into buildings, attracted as they are to light in darkness. The journal British Birds points to a cocktail of problems it causes: a “year-long cycle of light is one of the most important environmental cues for birds, and they synchronise their internal clocks with light to time their daily and seasonal foraging, communication, reproduction and migration,” it says.

Insects such as moths are also vulnerable, and not only by crashing into lights: “Flight-to-light behaviour can disturb local foraging, settling activity and longer-distance dispersal movements, potentially leading to high levels of mortality and reduced reproductive success,” according to the Journal of Urban Ecology in 2016.

If it is lighter at night, female moths produce fewer pheromones, attracting fewer males and mating less
If it is lighter at night, female moths produce fewer pheromones, attracting fewer males and mating less © Getty Images

Light pollution is growing globally at about 2.2 per cent a year, according to the journal Environmental Evidence, and in the UK there is rising concern. The Chief Medical Officer’s annual report in 2017 stated: “Local authorities have been replacing mercury and sodium street lights with LEDs. If this is done purely on the basis of energy efficiency and cost, it is possible to end up with installations that may not be fit for purpose.”

Blue-enriched LEDs can damage human and animal retinas as well as cause a multitude of problems for wildlife.

In 2014, a British Trust for Ornithology survey of 6,000 gardens found that urban birds wake later than their country cousins. So what will happen to the dawn chorus in towns?

This, incidentally, is one of the themes of a new work by the artist Alexandra Daisy Ginsberg. Her “Machine Auguries”, at Somerset House’s exhibition 24/7(see panel below), uses machine learning to generate artificial birdsong.

Artificial light causes urban birds to wake later than their rural counterparts, putting the dawn chorus at risk
Artificial light causes urban birds to wake later than their rural counterparts, putting the dawn chorus at risk © Science Photo Library

In fact, wildlife sensitivity to light types may point the way to a solution. Travis Longcore, associate adjunct professor at UCLA Institute of the Environment and Sustainability, has been working on the impact of artificial light on ecology since the turn of the century. He has designed an online tool listing commercially available lights that may have lower impact on wildlife at fluxometer.com/ecological/.

His research looked at insects, young salmon, the seabird Newell’s shearwater and juvenile turtles. Longcore found that the worst night-time lights for wildlife are intense blue and white colours — some affect species as much as the sun’s light spectrum. These are three times more disruptive than yellow or green lights.

The worst artificial lights for wildlife are intense blue and white colours
The worst artificial lights for wildlife are intense blue and white colours © Getty Images/iStockphoto

In many respects, light is the easiest form of pollution to curb — it’s a matter of restricting the use of artificial light and only using wildlife-friendly wavelengths.

In May 2019, the Social Science Research Network published some simple solutions in areas affected by artificial lighting.

Conservation efforts should, they advise, “be directed towards the following methods of spatial mitigation: limiting illumination to desired areas such as sidewalks or roads; dimming light sources to the lowest acceptable intensity; and — perhaps most importantly — reducing the number of fixtures installed in and around ecologically vulnerable areas.”

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Whatever the method they choose, gardeners and anyone else using artificial light at night need to act fast.

The statistics about wildlife decline make gloomy reading for gardeners in need of bees, birdsong and pest predators. In September 2019, Science magazine reported that bird populations alone have fallen by nearly 3bn across North America — an overall decline of 29 per cent from 1970.

UK government statistics show that the wild-bird population fell by 11 per cent from 1970 to 2018, with particularly heavy falls among turtle doves, whitethroats, lesser spotted woodpeckers and nightingales.

But for anyone unmoved by the idea of gardens without nightingales, newts and moths, there is a financial driver to the argument. According to the website ScienceDirect: “Light pollution generates significant costs including negative impacts on wildlife, health, astronomy, and wasted energy — which in the US amounts to nearly $7bn annually.”

Disappearing birdsong: a chorus of disapproval

Caption: Machine Auguries, 2019. Installation shot from 24/7 exhibition at Somerset House, London,   open 31 Oct 2019 – 23 Feb 2020. Commissioned by Somerset House and A/D/O by MINI. With additional support from Faculty and The Adonyeva Foundation. 
Artist Credit: Alexandra Daisy Ginsberg. 
Year: 2019
			Photo Credit: Luke Andrew Walker for A/D/O

Commissioned by Somerset House and design incubator A/D/O by MINI, Alexandra Daisy Ginsberg’s “Machine Auguries” looks at how our inability to switch off is damaging our world, reports Lucy Watson.

“I didn’t know of the effects on birds until I started the research, and I couldn’t believe what I found,” she says. Even the sounds produced by street lights affect their behaviour.

The installation is a recorded dawn chorus that merges into a song created by machine learning, symbolising the loss of the chorus. Ginsberg drew on the work of Richard Beard, who recorded birdsong in London’s Stoke Newington against the din of traffic, and Geoff Sample in Northumbria.

Birdsong used to be “so much denser”, she says. “We’re not really aware of what we’ve lost because it happens over time.

“The more I’ve had to learn for this project, the richer the countryside and the birds I can hear. It’s opened up for me a whole sound spectrum.”

‘Machine Auguries’ is part of the ‘24/7’ exhibition at Somerset House until February 23

Jane Owen is an FT Weekend contributing editor and the author of various garden books

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