Keeping the Lights on Leads to Sick and Tired Wildlife

By: Manraj Sagoo

While city lights may be beautiful, they can wreak havoc on urban wildlife. Imagine you had a neighbor that kept bright lights on all day and night. This situation would not be very pleasant. Well, for many animals that live in urban cities, we are that annoying neighbor. While we can simply close our blinds, urban animals do not have that luxury. Most plants and animals, including humans, rely on the daily cycle of light and dark to help regulate sleep, migration, mating, and other behaviors. Artificial lights at night (ALAN), like those that light up city streets, can disrupt the daily cycle of animals that live near them.

While we know that ALAN negatively affects urban wildlife, it still isn’t known exactly how this happens. A team of researchers led by Dr. Ann-Kathrin Ziegler from Lund University wondered exactly this, so they set out to get some answers. Ziegler’s team built a study that focused on understanding the specific effects ALAN had on a common urban bird, the wild great tit (Parus major). The team of researchers exposed great tit nestlings (i.e., great tit babies) to ALAN for several consecutive nights and then tested their blood. The researchers also tested the immune response of the birds studied.

The researchers found that birds exposed to ALAN had disrupted sleep cycles. These birds were not getting the rest that they needed to function normally. Disrupted sleep can lead to decreased energy levels, impairing their ability to hunt for food. Ziegler’s team found that disturbed sleep can also lead to a decreased immune response, making it harder for the birds tofight infections and viruses. The immune systems of great tit nestlings are particularly vulnerable to the effects of ALAN, as they are still developing. Interestingly, these findings are similar to what has been previously observed in other ALAN-exposed animals, including humans.

So, this begs the question, how does exposure to ALAN lead to these effects? Well, Ziegler’s team thinks that these effects are due to the hormone melatonin. Melatonin is a very important hormone that controls the sleep and wake cycle, along with other things. ALAN-treated birds in this study produced much less melatonin compared to birds that were not exposed to ALAN. Reduced melatonin production explains why the ALAN-treated birds could not sleep well. It is this lack of rest that might also explain why these birds had weaker immune systems.

Overall, Ziegler and her team’s research can help us understand exactly why wildlife, and humans, are known to be negatively affected by ALAN. Ziegler’s study shows a link between ALAN exposure, a lack of melatonin production, and a decrease in immune health. The disruption of the great tit’s sleep cycles along with a weaker immune system caused by ALAN is very concerning, as it may negatively impact their long-term survival as a species. Ultimately research like this brings to light the scale of human civilization's impact on nature. Even something seemingly simple, like lights being on at night, can drastically impact the animals we share this earth with.

Ziegler, A. K., Watson, H., Hegemann, A., Meitern, R., Canoine, V., Nilsson, J. K., & Isaksson, C. (2021). Exposure to artificial light at night alters innate immune response in wild great tit nestlings. Journal of Experimental Biology. 224 (10), jeb239350.