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.

 

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.

 

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