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Dark Skies – A Case for Turning Off the Lights

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By Karena DiLeo, Stewardship Coordinator

We as humans have a habit of modifying our surroundings to better suit our needs to the detriment of our natural environments. 

Sometimes it’s difficult to make the best decision to reduce our impacts in a world we have designed for consumption, but perhaps it can be as easy as turning off a light switch. Nighttime artificial lights disrupt the critical behaviors of both plants and animals and can have community-wide impacts, from earlier bud burst in plants to changing activity patterns in animals 1. Ecological communities are organized by daily and seasonal light cycles. By lessening the difference between day and night we are altering how species interact, which impacts their long-term survival 2.

Perhaps the most widely known impact is on songbirds, waterfowl, and seabirds during their spring and fall migrations between summer-breeding and winter-feeding habitats. During these long-distance, nighttime flights, birds rely on their complex navigational systems which include phototaxis, the movement towards or away from light. Light pollution disrupts these flights, leading birds off course and causing millions of deaths as birds collide into illuminated buildings and communication towers 3. Light pollution disrupts their circadian rhythms (internal clocks), alters their reproduction times, and changes flight behavior 4.

Bats synchronize their feeding intensity with the lunar cycle, decreasing activity on full moon or brighter nights5. This change in behavior has translated to bats altering their flight routes in response to light pollution6, most likely to avoid nocturnal predators.

Nighttime lights surrounded by buzzing insects and moths are a common summertime sight, however, light pollution is one of the greatest drivers of insect decline worldwide (along with habitat loss and pesticide use). Scientists have found that one third of all insects drawn to lights die before morning from predation, exhaustion, or collision with vehicles7. These artificial lights affect seasonal and daily movements of insects, reducing foraging, altering reproductive timing, increasing the risk of predation7, and even delaying diapause (dormancy) which increases winter mortality8. The impact on bioluminescent insects, like lightening bugs, is even more stark as light pollution hinders the male’s ability to locate females for reproduction9.

Ninety-nine percent of the United States has light polluted skies, with nearly eighty percent of North America unable to see the Milky Way10. But the good news is that unlike most other forms of pollution, by reducing usage or turning off our lights, we can fix the issue – no long-term clean-up needed. Once the skies are dark again, the natural world can begin to repair itself and we can anticipate a safer environment for all wildlife, including the beloved lightening bug.  

Common eastern firefly (Photinus pyralis). Courtesy weaver1234 on Getty Images/Canva.
  1. Sanders D., Hirt M.R., Brose U., Evans D.M., Gaston K.J., Gauzens B., and R. Ryser. 2023. How artificial light at night may rewire ecological networks: concepts and models. Phil. Trans. R. Soc. B. 378.
  2. Gaston K.J., Duffy J.P., Gaston S., Bennie J., & T.W. Davies. 2014. Human alteration of natural light cycles: causes and ecological consequences. Oecologia (176): 914-931
  3. Van Doren B.M., Willard D.E., Hennen M., Horton K.G., Stuber E.F., Sheldon D., Sivakumar A.H., Wang J., Farnsworth A., & B.M. Winger. (2021), PNAS 118(4)
  4. Cabrera-Cruz S.A., Smolinksky J.A., & J.J. Buler. 2018. Light pollution is greatest within migration passage areas for nocturnally-migrating birds around the world. Scientific Reports 8:3261
  5. Li H., Allen P., Boris A., Lagrama S., Lyons J., Mills C., Moussi P., Nichols C., Tacosik C., Tsaousis M., Wilson N.L., Grider J.F., Parker K.A., & M.C. Kalcounis-Rueppell. 2024. Artificial light at night (ALAN) pollution alters bat lunar chronobiology: insights from broad-scale long-term acoustic monitoring. Ecological Processes 13:13
  6. Stone E.L., Jones G., & S. Harris. 2009. Street lighting disturbs commuting bats. Current Biology 19:1123-1127
  7. Owens A.C.S., Cochard P., Durrant J., Farnworth B., Perkin E.K., & B. Seymoure. 2019. Light pollution is a driver of insect declines. Biological Conservation 241
  8. Merckx T., Nielsen M.E., Kankaanpaa T., Kadlec T., Yazdanian M., & S.M. Kivela. 2022. Dim light pollution prevents diapause induction in urban and rural moths.  Journal of Applied Ecology (60) 1022-1031
  9. Bird S. & J. Parker. 2014. Low levels of light pollution may block the ability of male glow worm (Lampyris noctiluca) to locate females. Journal of Insect Conservation 18:737-743
  10. Falchi F., Cinzano P., Duriscoe D., Kyba C.C.M., Edvidge C.D., Baugh K., Portnov B.A., Rybinkova N.A.& R. Furgoni. 2016. The new world atlas of artificial night sky brightness. Science Advances 2(6)