Artificial night lighting is disrupting the natural world

Artificial night lighting is causing widespread impacts to wildlife, according to researchers at the University of Exeter. The team analyzed more than 100 relevant studies and found consistent evidence of physical and behavioral changes in animals, particularly related to their hormone levels and sleep-wake cycles.

In every animal species studied, levels of the sleep-regulating hormone melatonin were reduced by exposure to artificial lights.

The researchers said that artificial night lighting has a diverse range of effects across the natural world, and should be limited whenever possible.

“Lots of studies have examined the impacts of artificial night-time lighting on particular species or communities of species,” said study co-author Professor Kevin Gaston. “Our research brings those studies together – and we find the effects are very diverse and very pervasive.”

“Particularly strong responses are seen in hormone levels, the timing of daily activity in diurnal (daytime) species, and ‘life-history’ traits such as number of offspring.”

“People may imagine this is all about powerful light, but in fact we are seeing a lot of responses at quite low levels of artificial light.”

Dr. Dirk Sanders said the differences were found in both animals that are active during the day and those that are active at night. 

“For rodents, which are mostly nocturnal, the duration of activity tended to be reduced by night-time lighting,” said Dr. Sanders. “In contrast, for birds – with all of those included strictly diurnal – artificial light led to an extension of the duration of their activity, with singing and foraging starting earlier.”

Previous studies have shown that artificial night lighting has a broad scope of impacts, ranging from reducing pollination to tricking trees into budding earlier in spring.

Just like climate change, night-time lighting appears to benefit some species in certain locations, but Professor Gaston said the clear message of the study is to reduce lighting where possible.

“Both climate change and night-time lighting are human-driven and enormously disruptive to the natural world. Historically, we have not really worried about the impact of night-time lighting. Only now are we discovering its wide-ranging effects,” said Professor Gaston.

“Our study shows that we should, as a matter of principle, only use night-time lighting where we need it and no further, and at intensities that we need and no more. In effect, we need to view light like any other pollutant.”

“Obviously it would be ridiculous to say ‘switch the world’s lights off’ – but we could reduce our use of light immensely with absolutely no impact on ourselves.”

Professor Gaston is the scientific advisor on an upcoming natural history series called Earth at Night in Colour, which will be released on Apple TV+ on December 4th.

The study is published in the journal Nature Ecology & Evolution.

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By Chrissy Sexton, Earth.com Staff Writer