Laetitia Nunny and Mark Simmonds
Do you ever look up at the night sky and feel that the stars are disappearing; and somehow, they seem less bright than they used to be? This is one facet of a phenomenon coming increasingly into focus as a significant threat to wild animals: light pollution. We are increasingly illuminating huge swathes of our planet. Seen from outer space in images taken by satellites, our cities shine in the nighttime darkness, our roads are marked by bright beads of lights, factories, monuments and sports stadiums are brightly illuminated and, even far offshore, spots of bright illumination mark oil platforms and the transit of ships. All this light is for our convenience and safety but much of it is not really needed and much leaks into the wider environment. We humans are creatures of the light and we evolved to be active during the day. We certainly don’t see as well in the dark of night as many nocturnal and crepuscular animals that are adapted to do so. Your cat can see much better in dim illumination than you can. And so, we beam bright light into our homes, streets and workplaces to help us find our way around and to allow us to continue to work and play long after our physical abilities would allow us without this unnatural illumination. Light is also important for our sense of safety and security.
Our rhythms of activity are mainly day (light) active and night (dark) resting. This is important for our health and welfare, and we have internal physiological systems that help maintain our cycles of activity. When we change time zones, for example via a long-haul flight into a very different time zone, we often struggle to function well. This ‘jet lag’ is a reminder of our normal day-set physiology. All other animals also have internal ‘clocks’ that are set by the natural light cycle and it is increasingly clear that by exposing them to unnatural light at unnatural times we are disrupting their lives and the consequences of this are surprising and deep.
For example, birds exposed to artificial light at night may interpret it as a longer period of daylight. Or they may end up migrating earlier and arriving at their breeding grounds earlier, which could have negative consequences if the resources they need for breeding are not yet available for them.
Bats are famous for being active at night, but their activities can be disrupted by artificial light at night, for example when a row of streetlights blocks their access to a foraging area or drinking site.
Insects, which are essential to the normal functioning of our terrestrial ecosystems, including for example as prey for many bigger species and pollinators of many plants, are in decline worldwide and there is growing suspicion that light pollution is implicated in this. Consider all those insects that gather around streetlights on a warm summer’s night. These may just be amusing for us but it can be lethal for them.
And what does light pollution mean for sea creatures? Studies in the sea lag behind those on land, but the first global atlas of light pollution in the seas and oceans was recently published showing that large areas are affected. At a depth of 1m, 1.9 million km2 of coastal seas are exposed to light pollution that will have a biological impact. Fast growing areas of coastal urbanization and intensive offshore development cause the greatest exposure. The critically endangered European eel, which has an extraordinary lifecycle whereby it migrates from rivers in Europe to the Sargasso Sea where it spawns, has to pass through areas which are lit by artificial light and, as they prefer dark routes, the timing of their migration could potentially be disrupted. Female sea turtles typically return to the beach where they themselves hatched to lay their eggs but they can be deterred by the presence of lights along beachfronts meaning that the density and the arrangement of nests can be impacted as the females try to nest in the areas with least light. Then, when it’s time for the baby turtles to hatch and make their way out to the ocean, the hatchlings can become confused by artificial lights which lure them in the wrong direction. Turtle hatchlings need dark landward silhouettes and the brighter light of the seaward horizon to orientate themselves and help them find the sea. They end up wasting valuable energy and are at risk of being taken by predators when they head in the wrong direction. These are just some examples but other aquatic animals are surely being impacted too.
The potential harm to species and habitats by light pollution clearly deserves more consideration.
In summary, what in many instances is just a convenience for our species can be lethal for so many others. However, now that this issue is increasingly recognized in many countries and regions, steps are being taken to reduce light pollution. Simple actions like directing light sources downwards and only using lights where they are needed, can make a real difference. And there can be benefits for our species too. Less intrusion of unnecessary light to affect our sleep cycles and, hopefully, in many areas the return of the stars in all their heavenly beauty.
OceanCare is concerned about the effects of light pollution on aquatic species in particular and contributes on this issue within the scientific conservation fora where measures to address this threat are being developed, and looks forward to their implementation.
- Azam, C. et al. (2018) Evidence for distance and illuminance thresholds in the effects of artificial lighting on bat activity. Landscape and Urban Planning 175: 123-135.
- Dominoni, D.M. and Partecke, J. (2015) Does light pollution alter daylength? A test using light loggers on free-ranging European blackbirds (Turdus merula). Philosophical Transactions of the Royal Society B: Biological Sciences 370(1667): 20140118.
- Owens, A.C.S. et al. (2020) Light pollution is a driver of insect declines. Biological Conservation 241: 108259.
- Price, J.T. et al. (2018) Exploring the role of artificial lighting in loggerhead turtle (Caretta caretta) nest-site selection and hatchling disorientation. Herpetological Conservation and Biology 13(2): 415-422.
- Smith, R.A. et al. (2021) Pre-migration artificial light at night advances the spring migration timing of a trans-hemispheric migratory songbird. Environmental Pollution 269: 116136
- Smyth, TJ, et al. (2021) A global atlas of artificial light at night under the sea. Elementa: Science of the Anthropocene 9(1): 00049
- Vowles, A.S. and Kemp, P.S. (2021) Artificial light at night (ALAN) affects the downstream movement behaviour of the critically endangered European eel, Anguilla anguilla. Environmental Pollution. 274: 116585.
Director of Science