Under the Spotlight
Why Designing with Dark Skies Compliant Lighting Plays a Crucial Role in Protecting our Wildlife - by Freyja Austin
Part 2 of this feature on artificial light at night (ALAN) will look at how the light in your garden can impact your resident wildlife community. In an attempt to help protect local wildlife we may hang bird feeders, plant pollinator friendly flowers, or install bug hotels in our gardens. However, many are unaware that one simple garden feature, night lighting, may be deterring and even negatively impacting the wildlife on their doorstep. Below are some reasons for responsibly lighting our gardens at night:
~69% of mammals are nocturnal.
Visits to flowers located near artificial light by nocturnal pollinators has decreased by 62% in some areas.
Caterpillar populations in areas lit by streetlights have declined by 52%.
Our gardens are home to many nocturnal species, some of which, like hedgehogs, bats, and doormice, are in decline. By incorporating dark, natural spaces into gardens we can minimise humans effect on these struggling species.
Wildlife and Wild Light
Life evolved under cycles of natural light and darkness, therefore, on a large scale and a residential scale wildlife is undoubtedly suffering due to ALAN. Light impacts organisms at an individual and population scale but can also have consequences for whole ecosystems. Humans see a range of wavelengths that we call “visible light”; these wavelengths make up only a small part of the electromagnetic spectrum. Different organisms see varying wavelengths of light that differ from those which we see, some can even see more. Their sensitivity to light therefore differs from ours, meaning even very low light levels can affect animals more severely than we may realise.
Night or Day
Birds like the robin have been observed breaking away from the dawn and dusk choruses, as artificial light leads to singing earlier in the morning and later at night.
One of the main impacts of light at night is its interference with animals’ circadian rhythms. Also referred to as our internal clock, circadian rhythms are repeating 24-hour cycles that our brain functions under to regulate processes like hormone production, wake and sleep, and alertness. These rhythms are responsive to light and dark cues, and as ALAN can put areas into longer sessions of light (in essence creating shorter nights or even permanent day conditions) it can interfere with these rhythms, and by extension vital internal processes in animals. Below are some further examples of how ALAN can impact animal and plant life:
Diurnal and seasonal light cycles dictate the initiation of events such as foraging and hunting, breeding, emergence from hibernation, and migration. ALAN can alter the timing of these events.
Predation can increase as many prey species use the cover of darkness as protection.
Many migratory bird species use natural light cues to navigate along migration routes and may lose their way if these cues are obscured by ALAN.
Pollination may be reduced as many insect pollinators are wholly nocturnal and will avoid light.
Artificial lighting can create a barrier that light avoiding species will not cross, thereby fragmenting the habitat.
Nearly every species studied by scientists has shown to be impacted in some way by ALAN; it is important to know how so that we can mitigate the effects and support the wildlife on our doorstep. One animal that has been subject to many investigations into the effects of light at night, and for which we have a clearer idea of the impacts, is the bat.
“Turn on the Dark, I’m Afraid of the Light”
This line from Shel Silverstein’s poem ‘Batty’ has some truth to it, as bats make up 1/3 of all nocturnal species. They are evolved for the dark, their vision is specialised to low light levels, and therefore they are very sensitive to even low levels of ALAN. Bats will shelter in roosts during the day and at night use commuting routes to fly to feeding areas, where the darkness provides them with protection from predators. Most species of bats are light avoiding, although the few that are not have been seen to hunt under artificial lights where insects will congregate. This may seem advantageous; however, bats natural predators like peregrine falcons have been observed predating bats who are exposed under these lights.
Bats are ecosystem supporters, they regulate insect numbers, disperse seeds, and pollinate plants, and in the UK all species are protected under the law.
Many bat species, including the UK’s rarest, are lighting avoiding, so irresponsibly lighting your garden at night, if bats are known to reside in or travel through your local area, can be hugely detrimental. Light that shines near the entrance of roosts can delay bats emergence at night, sometimes by almost an hour, or trap them inside altogether. This can cause them to miss peak insect abundance (just after dusk) and reduces foraging time, which impacts their survival. Additionally, bats are known to use established commuting routes to fly from their roosts to feeding areas; if ALAN from gardens overlaps with these routes, again their foraging will be impacted. Additionally, light from gardens can interfere with bats natural visual cues which can prevent them from being able to find home, they may also choose to abandon illuminated roosts altogether.
As explained in part 1, artificial light at night can increase regional light pollution and can degrade an areas view of the sky. We have now looked at how artificial light can impact your garden ecosystem. In the final part of this feature, I will share with you the simple yet effective ways to install beautiful and functional outdoor lighting, while helping to conserve our view of the stars and lowering your impact on local wildlife.
Written by Guest Blogger Freyja Austin, Feb 2024
References:
https://www.buglife.org.uk/campaigns/light-pollution/
https://assets.publishing.service.gov.uk/media/5a7c47f8ed915d76e2ebc4e1/9780108508547.pdf.pdf
https://darksky.uk/wildlife-ecosystems/
https://darksky.org/app/uploads/2022/06/IDA-State-of-the-Science-2022-EN.pdf
https://www.gov.uk/guidance/light-pollution#possible-ecological-impact
https://education.nationalgeographic.org/resource/light-pollution/
https://royalsocietypublishing.org/doi/10.1098/rstb.2014.0124