Big City Bats

An LED Floodlight, Image by Leon Brooks. Retrieved from

Throughout the world, more and more people are living in urban areas. We’re called by the glimmering lights, the whirlwind of activity, the sights and sounds of the big city. Some of these same factors that draw people to cities are what drive other animals away–or, in many cases, cause harm to the animals who stay.

For bats, who are most active at night, urban light pollution can pose some major issues (Laforge et al., 2019; Langley, 2019; Seewagen and Adams, 2021). Artificial light can be disorienting for nocturnal animals, disrupting their circadian cycles and changing their typical activity levels throughout the day (Seewagen and Adams, 2021). Further, high levels of light leave species that are used to the cover of darkness vulnerable to predators (Cravens and Boyles, 2018; Laforge et al., 2019). Still, some bats–individuals or entire species–choose to spend more time foraging in lighter areas because UV lights attract their preferred food choice: insects (Cravens and Boyles, 2018; Langley, 2019; Seewagen and Adams, 2021).

So how does the presence of light impact the bats who choose to stay?

Seewagen and Adams (2021) found that several species of bats reacted to the presence of LED floodlights by greatly reducing their foraging activity. Migratory tree bats tended to not be impacted by light or even be attracted to it, while nonmigratory species tended to avoid light areas (Seewagen and Adams, 2021). Little brown bats (Myotis lucifugus) have been found to have difficulty avoiding obstacles in highly-illuminated areas, indicating that light may have some impact on their sensory systems, including systems involved in orientation (Seewagen and Adams, 2021).

Little Brown Bat, Image by Moriarty Marvin, USFWS. Retrieved from

Cravens and Boyles (2018) focused on the differences between levels of the blood metabolite beta-hydroxybutyrate in bats found in lit and unlit conditions. Beta-hydroxybutyrate is a fasting metabolite, and is used for energy in metabolic processes when triglyceride fat storage is low. Interestingly, this is not the exact case in bats: beta-hydroxybutyrate levels spike after feeding–so they are correlated with periods of intense exercise (Cravens and Boyles, 2018). For red bats (Lasiurus borealis), beta-hydroxybutyrate levels were highest just after sunset in highly-lit sites, while the opposite was true in dark sites (Cravens and Boyles, 2018). Cravens and Boyles (2018) suggest that red bats have altered their foraging activity to prey on insects at lit sites just after sunset, while other bats may forage throughout the night. Also, red bats captured at lights late at night had low levels of these blood metabolites, suggesting that they were able to gain more energy from well-lit areas with less work (Cravens and Boyles, 2018).

Despite this positive impact on foraging in some bat species, high levels of light pollution can negatively impact bat diversity and species abundance in urban areas (Laforge et al., 2019; Langley, 2019; Seewagen and Adams, 2021). Seewagen and Adams (2021) were only able to detect little brown bats on 14% of light nights, while they were able to hear little brown bats calling on 65% of dark nights. Laforge et al. (2019) had similar results, with artificial light being a significant predictor of bat presence and activity, as well as their ability to move through their landscapes.

While artificial nighttime light can provide light-tolerant bats with novel foraging opportunities, finding ways to mitigate the impacts of nighttime light can greatly improve bat biodiversity. The most obvious solution is to turn out the lights–reducing nighttime light can help bats expand their species range by providing opportunities to safely move between habitat patches (Laforge et al., 2019). With less light, bats will be better able to avoid predators, and their sensory systems and circadian cycles may fall back in line. However, reducing light is not enough to truly improve bats’ habitat quality (Laforge et al., 2019)–and it is not the only option. Increasing urban greenspace can provide bats with shelter from predators in the form of tree canopy cover (Langley, 2019). Bats may even be able to strike a balance–enjoying the benefits of insects attracted to UV lights while remaining safely covered (Langley, 2019).

Whatever the solution may be, one thing is for sure: providing safe habitats for bats is necessary for supporting pollination, controlling insect populations, and preserving biodiversity in a changing world.

Works Cited

Cravens, ZM & Boyles, JG (2019) Illuminating the physiological implications of artificial light on an insectivorous bat community. Oecologia 189:69-77. doi: 10.1007/s00442-018-4300-6

Laforge, A, Pauwels, K, Faure, B, Bas, Y, Kerbiriou, C, Fonderflick, J, & Besnard, A (2019) Reducing light pollution improves connectivity for bats in urban landscapes. Landsc Ecol 34:793-809. doi: 1o.1007/s10980-019-00803-0

Langley, L (2019, April 17) Light pollution hurts urban bats. Trees can help. National Geographic.

Seewagen CL & Adams, AM (2021) Turning to the dark side: LED light at night alters the activity and species composition of a foraging bat assemblage in the northeastern United States. Ecol Evol 11(10):5635-5645

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Image 2 source:

“Hey! Turn that light off!” – Sea Turtles and Light Pollution

Sea turtles (Cheloniidae and Dermochelyidae families) are beloved by many, featured in animated kids movies like Finding Nemo as well in many viral videos showing newly-hatched babies scurrying into the ocean. Many people who live near them know they are endangered and care about them. What they don’t know is that their back porch light to their beach house is causing trouble. Artificial light pollution is a relatively new threat for sea turtles, disrupting many of their physiological functions.

Florida’s beaches are where many sea turtle species call home, nesting under the sand in the dunes. As beach tourism in the state continues to grow, more and more artificial light is spreading along the coastline, threatening these nesting sites. The artificial light disrupts the turtle’s circadian rhythm, confusing them if it is nighttime or daytime, making them more vulnerable to nocturnal predators who catch them unaware (Hu et al., 2018). In addition, when baby turtles are hatching, light pollution can disorient them during their dash to the ocean (Long et al., 2022). Geo-spacial collected data shows, however, that sea turtles are already avoiding areas of high light pollution (figure 1). Therefore, continued expansion of lights along Florida’s beaches could continue to reduce usable habitat for sea turtle nesting activities.

Figure 1. Geo-spacial map of artificial light on the Florida coast vs. density of Loggerhead turtle nests (Hu et al., 2018)

Luckily, the people of Florida have the sea turtles backs. Legislation exists that prohibits certain wavelengths of light to be visible from the beach, requiring shielding of exterior light bulbs (Mascovich et al., 2018). Education programs are also conducted to inform tourists who may be staying at a place close to the beach, informing them to turn off their exterior lights at night to protect nests. These programs are conducted with mixed success, however, with guests often still leaving their lights on throughout the night (Mascovich et al., 2018).

New lighting technology has also recently become an idea of preventing further and reducing current light pollution. For example studies show that Loggerhead sea turtles (Caretta caretta) are generally more sensitive to shorter wavelengths of light at less than 560 nanometers (Long et al., 2022). Thus, the state of Florida has been testing a new 624 nanometer lamp to use along coastal highways, to try and reduce light pollution that highways create. A study conducted by Long et al. showed that these new lamps DO work, with hatching turtles finding their way to the ocean just fine (2022).

Overall, while these solutions do work, they are not strictly enforced. There must be more legislative action and encouragement to use higher frequency light near the nesting locations to reduce light pollution.


Hu, Z., Hu, H., & Huang, Y. (2018). Association between nighttime artificial light pollution and sea turtle nest density along Florida coast: A geospatial study using Viirs Remote Sensing Data. Environmental Pollution, 239, 30–42.

Long, T. M., Eldridge, J., Hancock, J., Hirama, S., Kiltie, R., Koperski, M., & Trindell, R. N. (2022). Balancing human and sea turtle safety: Evaluating long-wavelength streetlights as a coastal roadway management tool. Coastal Management, 50(2), 184–196.

Mascovich, K. A., Larson, L. R., & Andrews, K. M. (2018). Lights on, or lights off? hotel guests’ response to nonpersonal educational outreach designed to protect nesting sea turtles. Chelonian Conservation and Biology, 17(2), 206.