Writer: Bejan Yilmaz
Light pollution has acquired considerable status as an environmental concern over the last two decades, involving excessive and misdirected artificial light in the environment. Humans use artificial lighting as a necessity for daily activities, while this extra light interferes with ecosystems that normally affect nocturnal animals. Nocturnal animal activity depends on natural darkness to carry on such behaviors as hunting, reproduction, and locomotion. These natural processes can be disrupted when artificial light floods an environment, and the effects on individual species and broader-scale ecosystems can be negative.
Fig.1. Growth in light pollution over time by treatment group status. This figure shows the percentage of cells with a DMSP-OLS ADN > 5 from 2000 to 2012, divided into two groups based on whether a horizontal well was drilled within the study period. In 2000, neither group had cells with DMSP-OLS > 5, as per the initial design. (ResearchGate, 2021)
Whereas many nocturnal species, such as owls and bats, predators utilizing highly adapted night vision to hunt in the dark, consider darkness a constituent key to their survival, prey animals rely on the protective cover of darkness to avoid being eaten. Artificial lighting interferes with this process. For example, research has shown that streetlights and building lights make some prey species more visible and easy targets for predators. Predator populations may benefit temporarily but, in the long term, such imbalances can destroy local ecosystems through the unnatural development of one population at the expense of others (Gaston et al., 2013).
Light pollution interferes with the navigation ability of nocturnal animals. Many species, including migratory birds and sea turtles, use natural light as a means of orientation. For example, hatchlings of marine turtles naturally move toward the sea through inherited locomotion; the sea is, predictably, a natural reflector of moonlight. When this natural light source becomes surpassed by artificial ones from proximal buildings, the hatchling turtles move inland, reducing their survival rate greatly. This disorientation not only causes individual harm to animals but also threatens whole populations, especially for already at-risk-of-extinction species (Witherington et al., 2000).
Light pollution can also interfere with mating behaviors of nocturnal animals: many species depend on the dark as a cue that it is a safe time to call or to display behaviors to attract mates. Fireflies, for instance, depend on their bioluminescent signals in complete darkness to communicate and find mates. Bright artificial lights can drown out their natural glow and interfere with their communication. Such is the case, wherein fireflies have quickly disappeared in those regions with heavy light pollution due to their inability to locate their potential mates successfully. This, in turn, impacts their successful reproduction, which could have long-term effects on the population dynamics and biodiversity in these affected regions (Owens et al., 2018).
Artificial light interferes with the circadian rhythm, which refers to an internal biological clock that signals the sleep/wake-up cycles of animals. Light at night is artificial and can mislead such rhythms, turning animals active at the wrong times. For instance, several species of birds are recorded to sing earlier in the daytime in artificially illuminated regions; this can surely disrupt their natural rhythm and sometimes even wear out the birds (Dominoni, 2015). Other nocturnal animals may shift their activity levels or shift hunting time, leading to imbalances in food availability and energy expenditure.
Light pollution affects not just individual nocturnal species but also whole ecosystems. Plants that rely on nocturnal pollinators, for example, moths, may have plants that rely on these animals disrupted due to disrupted light pollution. Nocturnal pollination played a very important role in the reported reproductive success of diverse plant species (Knop et al., 2017). If these pollinators are drawn away from natural areas due to artificial lighting, then the plants would be left with reduced pollination rates. This can affect plant populations and species dependent on those plants.
The effects of light pollution on nocturnal animals can best be minimized by a combination of community awareness and practical solutions. Among these are motion-sensor lighting, shielding lights to reduce skyward glow, and choosing lights with warm hues. All the measures mentioned earlier are particularly effective in the cities lying in the vicinity of the sensitive nocturnal species' habitats. By addressing the very roots of light pollution, the communities are at an advantage in safeguarding nocturnal wildlife and maintaining the fragile balance of natural ecosystems.
To summarize, light pollution has become a serious threat to nocturnal animals. Artificial light impacts everything from the navigation errors of migratory birds and sea turtles to the disruption in mating by fireflies. It is an issue that needs attention in the interest of biodiversity and furthering the opportunities for nocturnal species to continue their roles in ecosystems. With the growing awareness of light pollution impacts, practical lighting solutions can make a meaningful difference in protecting these vulnerable animals and their habitats.
References
Dominoni, D. M. (2015), The effects of light pollution on biological rhythms of birds: An integrated view, Philosophical Transactions of the Royal Society B: Biological Sciences, 370 (1667), 20140117.
Gaston, K. J., Bennie, J., Davies, T. W., Hopkins, J. (2013), The ecological effects of nighttime light pollution: a mechanistic appraisal, Biological Reviews, 88(4), 912-927.
Knop, E., Zoller, L., Ryser, R., Gerpe, C., Hörler, M., Fontaine, C. (2017), Artificial light at night as a new threat to pollination, Nature, 548(7666), 206-209.
Owens, A. C. S., Lewis, S. M. (2018), The impact of artificial light at night on nocturnal insects: A review and synthesis, Ecology and Evolution, 8(22), 11337-11358.
Witherington, B. E., Martin, R. E. (2000), Understanding, assessing, and resolving light-pollution problems on sea turtle nesting beaches, Florida Marine Research Institute Technical Report
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