Street Lamps Kill Mice – And Could Harm Humans

Entire colonies of mice risk dying within days, experiencing lower birth rates and suffering higher stress levels – all because they’re exposed to artificial light at night (ALAN).

Researchers say that for the first time they have clear evidence that light pollution can be extremely harmful to species of mice, and suggest they may be harmful to ecosystems, biodiversity, and even human health.

The team from Tel Aviv University placed nearly 100 mice of two species – the golden spiny mouse, and the common spiny mouse – in outdoor enclosures which simulated living conditions in the wild, like the natural light and dark cycle, humidity, and precipitation.

Six enclosures were exposed to different types of artificial light – like the light emitted from street lamps – over the course of the 10-month study. The mice were found to have experienced a variety of unexpected and adverse effects. 

Two of the enclosures that were exposed to white light saw all the mice dying within several days, both on separate occasions. 

Autopsies revealed no abnormal findings – leaving them to assume that ALAN had impaired their immune response to an unidentified pathogen. 

The light pollution also disrupted the mice’s reproductive success. They mostly breed during the summer when temperatures are high – but the light confused the common spiny mice, and led them to breeding year round, producing a lower number of pups per year.

And with the golden spiny mice, they kept breeding in the summer, but the number of young was reduced by half compared to the control group, which continued to thrive and breed normally.

Additional tests also found that the light caused physiological and hormonal changes, most significantly in the level of cortisol, an important stress hormone that helps regulate the immune system.

Exposure to blue light increased cortisol levels of golden spiny mice, while white light reduced cortisol levels of golden spiny mice males in winter.  

“Our findings show that light pollution, especially cold white and blue light, increases mortality and disrupts reproduction, and thus may be detrimental to the fitness and survival of species in the wild,” said Prof. Noga Kronfeld-Schor, Chief Scientist of Israel’s Ministry of Environmental Protection. She led the study.

“This adverse effect can have far-reaching consequences at the current wide distribution of light pollution. Our clear results are an important step toward understanding the impact of light pollution on biodiversity and will help us promote science-based policies, specifically with regard to the use of artificial light in both built and open areas. In future studies we plan to investigate what caused the extensive deaths in the enclosures exposed to ALAN, focusing on the effect of light pollution exposure on the immune system.”

The research was published in the academic journal Scientific Reports. 

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