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Effects of light pollution on Urban Black Swans

Effects of light pollution on Urban Black Swans

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As a continuation from the previous introductory post on light pollution, we look deeper into the impacts it has on bio-diversity, specifically wildlife that shares the urban space with us. As aforementioned, exposure to artificial lighting, specifically blue light, at night-time prevents the body from producing the sleep hormone melatonin. This is why it is worth once in a while to listen to mom and put your phone away before sleeping. Other lightings such as LED streetlights are also sources of blue light pollution.

Blue light pollution is known to cause sleeplessness in humans, but what about the urban wildlife? It was predicted that warmer, amber lightings with less short, blue wavelength helps in mitigating biodiversity impacts of light pollution, and cities have transitioned into adopting them. To test the validity of this prediction, animal behaviour researchers from Australia tested whether unfiltered white light (blue-rich) and filtered amber (blue-reduced) light from LED streetlights had any implications on the rest and melatonin production in black swans.

Fig 1: The cygnus astratus, or black swan, native to Australia (photo credit: google photos)

 

The swans are ideal test subjects as they are large and can be re-captured with ease. They are also diurnal, with relatively flexible sleep patterns. This meant that the black swans are relatively resilient to sleep disruption, hence the researchers predicted that if the swans are affected by the lights, then other more sensitive urban wildlife will have a greater impact. Quality of sleep of the swans were quantified using electroencephalogram (EEG) measurements and melatonin in blood levels. It is also good to note that the swans are exposed to urban lighting in a naturalistic manner, meaning the test site was constructed to be like a typical pond in the park.

The results of the study were unexpected; where the colour of the streetlights had no differing effect on the quality of sleep of the swans. The study also confirmed that the swans rested less under white night controls over dark controls, as seen from shorter rest durations (~30 mins less) and shorter REM sleep.

Fig 2: Results of light treatment affecting the sleep cycle of the swans (photo credit: Alusebrook et al. (2020))

 

There is much to take away from this. Several interesting explanations for these results were given. Firstly, it was suggested that perhaps the swans were more disrupted by amber lighting at night was the fact that unlike humans, the swans have greater visual sensitivity for light from the red and yellow spectrum, hence amber lighting for these diurnal animals might have further stimulated them at night. Melatonin levels in the swans were also non-conclusive due to the low levels detected overall, hence the study was unable to develop a conclusion linking melatonin production to colour of lighting for the swans.

Nonetheless, the results hinted that current mitigative measures of altering the colours of streetlights is not as effective as it was once predicted to be. It is therefore more advisable to turn off streetlights entirely, especially in parks, reserves, or where plenty of urban wildlife reside, to keep disruption from artificial light pollution to bio-diversity down to a minimal.

 

References

Aulsebrook, A. E., Lesku, J. A., Mulder, R. A., Goymann, W., Vyssotski, A. L., & Jones, T. M. (2020). Streetlights Disrupt Night-Time Sleep in Urban Black Swans. Frontiers in Ecology and Evolution, 8, 131. https://doi.org/10.3389/fevo.2020.00131

City of stars, there’s so much that I can’t see (literally)

City of stars, there’s so much that I can’t see (literally)

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Cities and bright lights are synonymous, and stunning nightscape are often an important feature of a vibrant and flourishing city. Indeed, cities are meant to be sparkling, but bright lights have robbed us of other wonders of the world. For example, we know for sure that stars exist above our heads in the sky, but why is it that we see nothing but pitch black when we tilt our head up to the skies at night in the city? In this blog post, we will be looking into the frequently overlooked phenomenon of light pollution.

 

What exactly is light pollution?

Fig 1: A faint glow can be seen in the night sky over the city. This is known as sky glow, when artificial light from the city is reflected on atmospheric particles (photo credit: skyglow project)

 

Throwing back to the definition of pollution I gave in the very first post; pollution is introduction of harmful materials into the environment, in this case, light is our pollutive substance. It is important to note that pollutive light mainly refers to artificial lighting, so no, we will not have to fight the sun when combatting light pollution. Light pollution is a major side effect of urbanisation, and is often an underlying contributor to various health implications and ecosystem disruptions.

 

Sleepless nights in a city that never sleeps

In a city, one is rarely shrouded in darkness. Take Singapore for an example, to ensure safety and visibility at night, almost every corner of neighbourhoods is illuminated by a street lamp. Although light acts as a safety mechanism in the urban setting, as it discourages criminal activity (NCPC, 2003), constant exposure to artificial light can be detrimental to the natural rhythms in living things. Humans have an internal circadian clock that regulate our sleep cycle through roughly 24 hours. Exposure to artificial light at night when the body is supposed to be sleeping causes the clock to delay the production of melatonin, the hormone that triggers drowsiness. Longterm disruption of circadian cycle will eventually result in insomnia and related illnesses such as stress and anxiety from the lack of rest (NIH, 2021). There was even a study that linked circadian disruption to being a carcinogen to humans (IARC, 2007).

 

Dancing in the streetlights?

Fig 2 & 3: Good samaritans helped to pick up the straying turtle hatchlings and bring them back to the coast. Some also parked their bicycles to cordon off the path to prevent more collision with the hatchlings (photo credit: Brendan Goh)

 

City light pollution also affects the wildlife that live close to or within urban environments. Many animals have the natural instinct to follow the sun or the moon for directional guidance, such as turtle hatchlings. Just recently in Singapore at Changi Beach, there was a sea turtle hatching event that caught the attention of the general public. Turns out, instead of moving towards the sea, the hatchlings mistook the park’s street-lamps as the moon, and made its way onto the bike paths, where many were crushed by unsuspecting cyclists. Thankfully, citizens noticed the tiny hatchlings and helped to divert and guide them back to the waters (Lee, 2021).

 

Do we turn off our lights at night then?

Of course it is not plausible to power off an entire metropolis at night time, however, there are still room for improvement in the current lighting structure of a city. For example, making the switch to energy-efficient and lower blue light LED street-lamps can decrease blue light exposure (which prevents melatonin release). Legislations can be established to control outdoor lighting, and sensors can be used for areas with less foot-fall. We can also do our part by installing blinds to prevent light trespassing.

 

 

References

International Agency for Research on Cancer. (2011, July 21). IARC Monographs Programme finds cancer hazards associated with shiftwork, painting and firefighting. https://web.archive.org/web/20110721001355/http://www.iarc.fr/en/media-centre/pr/2007/pr180.html

Lee, J. (2021, December 18). Sea turtles hatch near changi coast cycling path, passers-by rescue most of them. Must Share News – Independent News For Singaporeans. https://mustsharenews.com/sea-turtles-hatch-changi/

National Crime Prevention Council. (2003). CPTED Guidebook. https://www.ncpc.org.sg/cpted.html

National Institute of General Medical Science. (2021). Circadian rhythms. https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms.aspx#:~:text=Circadian%20rhythms%20are%20physical%2C%20mental,the%20study%20of%20circadian%20rhythms

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