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Animals in the dark

Light pollution and its effect on fauna

Published: 28 10月 2022
The impact of humanity on the environment sadly goes way beyond the well-known effects of our unbridled urbanisation, our deforestation adopted to make way for new farms or plantations, and the plastic waste we have dumped in our oceans. There is also a kind of pollution caused by humans that is more difficult to see straightaway because it is less apparent. This is the combined effect of light and sound pollution.

Even if they share the same environment, living organisms have different Umwelts, which means they experience the space around them in different ways. Umwelt is a term that describes a kind of sensorial bubble, and every species has its own one. This is the theory posited by Jakob von Uexküll, the pioneer of ethology and ecological sciences, who argues that every living organism exists in its own environmental world, that is closed but remains connected to others.

The evolutionary stimuli linked to the senses of animals and their surrounding environment are often disrupted by the actions of human beings, sometimes with lethal effects. Darkness, for example, is increasingly threatened by light pollution. The astronomer Pierantonio Cinzano has calculated that two thirds of the world’s population live in areas where nights are at least 10% lighter than natural darkness. According to his research, approximately 40% of human beings are permanently immersed in the equivalence of moonlight, while 25% live every night in an artificial twilight with a level of illumination that is even stronger than the moon.
A night in Beijing (Photo by Alexander Kaunas on Unsplash)
A night in Beijing (Photo by Alexander Kaunas on Unsplash)
In an environment in which darkness is increasingly threatened, even the lampposts that surround natural parks become a deadly hazard for insects, which confuse these artificial light sources with sunlight and end up flying around them until they are exhausted. Darkness is fundamental for the existence of numerous animals. The echolocation technique that bats use to move and hunt is a good example. These animals exploit darkness and the invisibility it gifts them with regard to both their prey and their predators by modulating sounds they emit from their noses and accurately decodifying the echoes that are bounced back.

Owls, moths, mosquitoes and various mammals have all evolved to live in a way that exploits darkness.
Thankfully, light pollution is easier and faster to combat than environmental pollution, like the plastic waste in our oceans. Even if we stopped filling our seas with bottles and bags tomorrow, there would still be thousands of tons of rubbish to clear up from the last century. But changing the kind of lighting or reducing it, produces an immediate effect and the problem disappears. Take LEDs for example. From an environmental point of view, LED lights reduce energy consumption significantly, but the cold light of high efficiency, white LEDs increases light pollution. There are, however, latest generation warm colour LEDs that offer a solution by zeroing or at least reducing the harmful effects that light can have on the sensorial bubbles of nocturnal animals like bats.

To understand the importance of light, in this case, natural light, Ed Yong, in The Atlantic and in his book An Immense World: How Animal Senses Reveal the Hidden Realms Around Us, focuses on the case of Lake Victoria researched by the evolutionary biologist Ole Seehausen. This body of water between Uganda and Tanzania is home to five hundred species of Cichlid fish that cannot be found in any other part of the world. So why is this location so unique? In natural light conditions, the deepest parts of the lake have a kind of luminosity that tends towards yellow and orange, while it stays blue where the water is deepest. The fish here have therefore always based their choices on light, which over time has created variety, including colour variety, in the species. So, the females who live near the surface prefer to mate with blue males, whereas the ones who reside in the deeper waters choose red males. Pollution over recent decades has led to the formation of new weeds that have made the water cloudy. This blocks the sunlight and therefore complicates the natural selection of the fish, causing a gigantic extinction of the species. The Cichlid fish in Lake Victoria is just one of the many stories that allows us to understand how sensorial pollution provokes a disconnect between living organisms and the cosmos.
According to Ed Yong, studying and understanding the senses of animals and the way in which they define their Umwelt is an effective way to «understand how we are spoiling the natural world and can also indicate ways to save it.»