LIGHT POLLUTION: A NUISANCE FOR PLANTS AND ANIMALS
The Mont-Bellevue in Sherbrooke, the Haut Saint François and the Granit MRCs around Mont-Mégantic, have initiatives to bring back the starry sky. The main objective is to enable people to admire the stars. Those human initiatives also have an impact on the species living in the area, both plants and animals and other solutions are available.
The alternating presence/absence of light acts like a clock on the biological activities of the livings. Have you ever stayed awake in front of a screen or reading with the light on for most of the night? Next day you feel the effects, but imagine if it happened every day! It’s a bit like what happens to plants and animals with light pollution. According to the MELCCFP [1] , light pollution is defined as “the light that is projected into the sky by the lighting of roads, businesses, houses, farms and historical monuments, making it difficult or even impossible to observe the stars and the Milky Way” (traduction from French). Thus, there is persistent unnatural light at night that “pollutes” the living environment of many species. This modulates gene expression, hormone levels, activity duration, behaviors and other aspects of life [2].
Picture Alex Fu
Impact on plants
Light pollution can cause early leaf loss or delay autumn leaf fall [3]. The presence of artificial light all year long in the dark can also lengthen the growing season [3]. Plants may also alter their phenology – the timing and duration of each life stage, such as flowering – as a result of this unnatural modulation of the light period [2].
Picture Audrey Thériault
Impacts on animals
Light pollution can disrupt the reproductive effort and limit the number of births, like for the turtles species [2][3][4] The presence of light sources on the opposite side of the sea also complicates the entry of young turtles in water, as they head for land rather than water. In flies and other insects, light from street lamps or other outdoor bulbs can exhaust, burn or kill them, as they are inevitably attracted to it [5]. Artificial light can also increase predation or shift the hunting time of predators. For example, insects flying around street lamps are more visible and more numerous, a luck for insectivorous birds and bats, who have no effort to find a meal that way. It can even lead some insectivorous species to choose a poorer quality territory to settle, because light attracts prey or makes it more visible [6]. It can even change the times at which they feed.
This light can also disrupt the migration of birds and fishes. They get tired by moving in the wrong direction, reducing the energy available for vital activities such as foraging. In one study, diurnals (day-living) birds experienced an increase in the time of activity and a decrease in sleep time in the presence of artificial light. On the contrary, in rodents, both diurnals and nocturnals, there is a decrease in activity time in the presence of light pollution. [2][3] In amphibians, artificial light can impose additional stress. Because these organisms use sunlight to warm their skin, too much light can dry out their skin [7].
Picture Nurefşan Koşar
Light pollution impacts several species, but it can also have several impacts on the same species, or groups of species. Butterflies, for example, are attracted by light, which distracts them from their normal activities. They therefore spend long periods twirling in front of a lightbulb, as if hypnotized, without ever detaching themselves from it. This makes them more vulnerable to predation [8][9]. Light will also alter their perception of flowers, and could lead butterflies to forage on less nutritious flowers. Light will also change the appearance of butterflies and the rest of the environment, which may mislead them into trying to reproduce with an object they believe to be a butterfly [8][10]! Light also artificially lengthens the day, which can mislead butterflies into initiating certain activities at the wrong time, such as migration [8][11] . Artificial light can also lengthen butterflies’ foraging period, allowing them to feed for longer periods [8].
Solutions
There are several ways to reduce light pollution. Individually, we can turn off our outdoor lights, choose lamps that constrain light to a smaller radius, choose bulbs with less intense brightness or wavelengths that are less disturbing for wildlife, or buy bulbs that only light when movement is detected. In terms of land-use planning, we could revandicate to turn off lights on businesses and sports fields at night, or propose the creation of a « Dark Sky Reserve », as Mont-Mégantic has done. Visit the Ciel Étoilé Mont Mégantic website for details of available solutions, including bulb type, intensity, colors and optimal temperature.
Light in the evening is essential for road safety and offers many benefits for people who work or travel at night. However, we must be aware that we share our environment with many species, and that their well-being is just as important as our own.
Picture Maurício Mascaro
[1] Environnement, Lutte contre les changements climatiques, Faune et Parcs (ELCCFP). (2024). La pollution lumineuse? Éclaire ta lanterne!. Gouvernement du Québec. www.environnement.gouv.qc.ca/jeunesse/chronique/2005/0503-causes.http
[2] Sanders, D. et al. (2020). A meta-analysis of biological impacts of artificial light at night.Nat Ecol Evol 5, 74–81. https://www.nature.com/articles/s41559-020-01322-x
[3] Hölker, F. et al. (2010). Light pollution as a biodiversity threat. A Cell Press journal.
[4] Dominoni, D. M. et al. (2015). Social cues are unlikely to be the single cause for early
reproduction in urban European blackbirds (Turdus merula). Physiology & Behavior 142 : 14-19. DOI: 10.1016/j.physbeh.2015.01.026
[5] Russ, A. et al. (2015). Seize the night: European Blackbirds (Turdus merula) extend their foraging activity under artificial illumination. Journal of Ornithology 156 : 123-131. DOI: 10.1007/s10336-014-1105-1
[6] McDonnell, M. et al. (2009). Ecology of Cities and Towns. Cambridge University Press,
Cambridge.10.1017/CBO9780511609763
[7] Gorenzel, W. P., et T. P. Salmon. (1995). Characteristics of American crow urban roosts in California. The Journal of Wildlife Management 59 : 638-645. https://www.jstor.org/stable/3801939
[8] Seymoure B. M. (2018). Enlightening Butterfly Conservation Efforts: The Importance of Natural Lighting for Butterfly Behavioral Ecology and Conservation. Insects 2018, 9, 22; doi:10.3390/insects9010022
[9] Beshkov, S. (1995). Butterflies and day-flying moths in light traps (Lepidoptera). Phegea, 3, 118–120. https://www.researchgate.net/publication/312027602_Butterflies_and_day_flying_moths_at_light_traps_Lepidoptera
[10] Kinoshita, M. et al. (1999). Colour vision of the foraging swallowtail butterfly Papilio xuthus. J. Exp. Biol. 1999, 202, 95–102. DOI: 10.1242/jeb.202.2.95
[11] Asch. V. (2007). Phenology of Forest Caterpillars and Their Host Trees: The Importance of Synchrony. Annu. Rev. Entomol. 2007, 52, 37–55. 10.1146/annurev.ento.52.110405.091418
