No matter how much you want to believe that most species sleep when we do, they don't! Nocturnal species are animals that are active at night. They sleep during the day and wake up at night. Their rhythm is set according to the changes in the day and night. The behavioral and biological activities like sleep-wake cycles, hunting, predation, breeding, reproduction, migration, etc., in many nocturnal animal species, are regulated by cues from light from natural light. Thus, their life functions are greatly affected by the nighttime metropolitan lights.
We have already discussed the general impacts of artificial lighting on wildlife here, but we rarely consider the fact that we need to protect dark skies in order to conserve wildlife, particularly nocturnal species. In this piece, we are going to have a detailed look at the impacts of nighttime lighting on nocturnal species and what we can do to conserve dark skies.
For thousands of years, the moon and stars were the primary sources of nighttime illumination. Now we humans have built huge cities and metropolitans which bustle with nightlife. The rapid urbanization by man is the key source of light pollution. We have harnessed energy in various forms. One of those forms is to use electricity to light up our spaces. But as human encroachment increases, ecosystems are getting disrupted.
Conforming to the World Atlas of Artificial Night Sky Brightness and National Geographic, 83 percent of the world’s population lives under skyglow. And about 99 percent of the population in the world’s most industrialized regions, the United States and Europe, can’t enjoy a natural night.
This excessive artificial light has compromised the lives and, most importantly, the pattern of life of animals, mainly nocturnal species. Hunters have adapted and evolved to see in the lowest of light, or they have strengthened their other systems like the hearing to catch their prey. The animals who are hunted have befriended shadows and have learned to use them to protect themselves from getting eaten.
There is a term for this form of pollution; ALAN or artificial light at night. ALAN is scattered light in the environment that is reflected in the ground. It causes troubles in various forms. The first form is the general increase in the light that negatively disrupts the rhythms and overall animals who are better suited for activities at night. Secondly, the intensity of the light emitted by these electric lights is different from the light emitted by the moon, which also adds to the injury it causes.
Cats, coyotes, possums, raccoons, and rats all come out of their homes to hunt, mate, and migrate. Aaron Schirmer, a biology professor at Northeastern Illinois University, noticed significant changes in these animals’ behaviors. They are now less active at nighttime and roam less in areas with lighting as dim as 6 lux (unit of light intensity). This is brighter than the full moon (0.108 lux) and slightly dimmer than the twilight’s glow (10.8 lux). Schrimer fears that these changes in movement patterns can expand to temporal and spatial levels, which would affect the food web in incomprehensible ways.
Adaptations in animals are also affected by light pollution. Nocturnal animals who hunt at night have adapted by having a special layer in their retina that reflects light and gives them the ability to see better at night. But now, when the artificial light comes into play, it overwhelms this little adaptation, and this light blinds them. This causes them to wander off their target or get lost during their hunting time. Most importantly, it affects their ability to hunt and therefore compromises their ability to survive.
Following the moon as a compass is a shared trait among a diverse range of fauna, including amphibians, reptiles, pollinating insects, birds, and mammals. But, with a 2.2% annual increase in artificial lighting, nocturnal animals are particularly vulnerable to nighttime skyglow who change their behaviors even with the slightest shift in light levels. We are familiar with many impacts of artificial nighttime lighting on animals.
Loggerhead sea turtles, for example, hatch at night and find the sea by sensing the faint light of the horizon. They crawl toward the horizon and ultimately find themselves in the ocean. But now, due to artificial light systems on the beach, they are unable to find the ocean. Their breeding success has also been reduced by 20 percent. Dung beetles also get disoriented in brightly lit landscapes which prevent them from seeing the stars. Moths fail at escaping bats, and clownfish fail to reproduce because they both need darkness. Other fish have been emerging earlier from their hideouts during the day and becoming prey.
Even the tiny sandhoppers are very responsive to changes in light levels. Sand hopper (Talitrus saltator) is a coastal crustacean found across the sandy beaches of Europe and also uses the moon as its guide. Sandhoppers bury themselves in the sand during the day and come out at night in forage for putrefying seaweed. In their research funded by Natural Environment Research Council, Daniela Torres Diaz and her colleagues demonstrated artificial skyglow disrupts the nighttime migration in this tiny amphipod crustacean, resulting in disoriented movement and limited migration towards the shore under the artificial skyglow. This way, they were missing out on feeding opportunities and their role as ecological decomposers.
This artificial light has been seen to affect amphibious creatures as well. The frogs and toads croak at nighttime. This croaking is essential for their reproduction. Now the artificial light at night time has increased so much that they can no longer reproduce in the dark.
Many other species like the caterpillar have been seen to be negatively affected by night lighting. The artificial light reduces the time for pupation in both sex of the caterpillar and also has been seen to reduce pupation mass.
Winter moths are important herbivores in deciduous trees. Their egg hatching is strongly associated with the bud burst in the springtime. But the premature bud burst in plants due to artificial light exposure disrupts the natural association between these two species.
Artificial light is also a threat to pollination. Many species of pollinating flies pollinate at night. They have adapted themselves to flying over flowers and pollination at night time. With the introduction of artificial light, they cannot determine the time of day, and the plants that depend on them for pollination do not get pollinated, which affects the reproductive power of the plant.
Let’s move our attention to the plants, which are the greatest producers in an ecosystem. It is these plants that help establish an ecosystem. Though they are not nocturnal, they are also influenced by artificial lighting. As we all know, plants use light for photosynthesis. And their primary source is sunlight. We also know that plants are complex creatures. They have established rhythms according to this change in light intensities in their surroundings; these are called circadian rhythms. Any change in the intensity and timing of light causes adverse effects on plant physiology and, therefore, on their growth.
Plants have established a period in which they get light from the sun, called a photoperiod. Now in the urban setting where there is exposure to artificial light, which contains more red wavelength radiation, this causes the deciduous trees to retain their leaves in the winter. This has been especially seen in trees or plants under the street light. The retention of leaves causes extensive damage due to the frost. These plants should normally shed all their leaves to survive the bitter cold but retain them, especially affecting the photosynthetic tissues.
Nowadays, there has been an increase in the use of the LED lights, which emit a more blue wavelength that causes early bud-burst in many species of plants. This early bud burst is highly harmful to the physiology of the plant, and buds that have now burst will not survive the conditions because they are not environmentally compatible. And even if they do survive, the time of pollination has not come yet, so the reproductivity of plants is extremely affected. Although it has been seen that periods of extensive dark periods can help plants re-establish their disrupted rhythms.
The solutions are very simple indeed in this case. First of all, there is a need to boast about the research for this particular subject. There has not been enough research conducted to fully understand the effects of this ALAN artificial light at night. Second, rapid education of the masses is essential for this purpose. They must be taught judicious use of artificial light. The public should be made aware of the harms of these lights. And an introduction and use of automatic systems which can turn off light when not in use can be incredibly beneficial for this cause. The introduction of dimmers and other technologies can be equally helpful. We must start to realize how human advancement and our unnatural transgression affect the ecosystems and the organisms living within them. So we can finally start to repair the damage we have been causing to our environment.
Schirmer, A.E., Gallemore, C., Liu, T. et al. Mapping behaviorally relevant light pollution levels to improve urban habitat planning. Sci Rep 9, 11925 (2019). https://doi.org/10.1038/s41598-019-48118-z
Bennie, J., Davies, T.W., Cruse, D., and Gaston, K.J. (2016), Ecological effects of artificial light at night on wild plants. J Ecol, 104: 611-620. https://doi.org/10.1111/1365-2745.12551
The biological impacts of artificial light at night: The research challenge May 2015 Philosophical Transactions of The Royal Society B Biological Sciences 370(1667):20140133 http://doi.org/10.1098/rstb.2014.0133
Nida Riaz is a freelance blogger based in Pakistan. She started writing about her passion for the environment when the world came to a stop in early 2020.