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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Anti-Anxiety Medication Increases Boldness in Atlantic Salmon

Timothy Knepp – USFWS National Digital Library

Atlantic salmon (Salmo Salar) are an important indicator of the health of marine ecosystems. Unfortunately, the sensitivity to poor environmental conditions which gives them their status as an “indicator species” also puts Atlantic salmon at risk, with many populations becoming classified as critically endangered, or even locally extinct (Oceana, n.d.).

Certain human activities can be a major problem for Atlantic salmon populations. Chemical pollution is one such issue that can be especially impactful in aquatic environments (Kolpin et al., 2002). Pharmaceutical drugs are particularly concerning, as most wastewater treatment plants are unable to completely remove pharmaceutical chemicals from wastewater (Nikolaou, Meric, and Fatta, 2007).

While pharmaceutical drugs are important for treating humans, livestock, and pets, many can also impact the physiology and behaviors of wild fish. Research on Atlantic salmon has shown that drugs found in surface water can disrupt individuals’ normal neural and endocrine system function (Hellstrom et al., 2016; Klaminder et al., 2019).

Oxazepam, a benzodiazepine drug used to treat anxiety disorders, is one drug that is found in many river systems (Hellstrom et al., 2016; Klaminder et al., 2019).  Oxazepam works by binding to GABA receptors in the body and changing the conformation of the receptors to allow GABA to bind more readily (Singh and Abdijadid, n.d.). GABA is a brain chemical that, when bound to receptors, inhibits brain signals that stimulate activity in the nervous system, so increased GABA binding reduces feelings of anxiety and stress (Singh and Abdijadid, n.d.).

In humans, benzodiazepines produce a sedative-like effect. In Atlantic salmon–as well as other migrating fish–the drug has a counterintuitive effect. Hellstrom et al. (2016) found that Oxazepam increases the rate of migration, and has been considered potentially positive for migration success in certain small-scale, laboratory studies.

So, why does a sedative drug seem to increase activity in salmon? Klaminder et al. (2019) attribute this speediness not to faster swimming, but to increased boldness. They found that Atlantic salmon treated with oxazepam were more likely to fall victim to predators along their migration routes (Klaminder et al., 2019). In other words, increased GABA binding induced by anti-anxiety medications can decrease predation risk perception in Atlantic salmon.

In an already vulnerable species, an increase in the chance of a fatal encounter with a predator can be a big deal–but are Oxazepam loads in rivers high enough to make Atlantic salmon bolder? Probably not (yet)–Klaminder et al. (2019) treated the fish in their study with a much higher dose than is currently found in waterways, and the authors suggest that their findings are not relevant to current pollution levels. But as drug manufacturing and prescriptions continue to increase, it’s important to consider how pharmaceutical pollution levels might increase in the coming years.

In the case of medication, there’s not a simple solution. Unlike other household products that contaminate waterways, reduced usage isn’t always an option. Instead, we need to focus on properly treating wastewater and increasing regulations of pharmaceuticals to prevent them from entering our waterways.

To learn more about how pharmaceuticals are regulated and treated in waterways, visit



Hellstrom, G, Klaminder, J, Finn, F, Persson, L, Alanara, A, Jonsson, M, Fick, J, & Brodin, T (2016) GABAergic anxiolytic drug in water increases migration behavior in salmon. Nat Commun 7. doi:10.1038/ncomms13460


Kolpin, DW, Furlong, ET, Meyer, MT, Thurman, EM, Zaugg, SD, Barber, LB, & Buxton, HT (2002) Pharmaceuticals, hormones, and other organic wastewater contaminants in US streams 1999–2000: a national reconnaissance. Environ Sci Technol 36(6): 1202-1211. doi:10.1021/es011055j
Klaminder, J, Jonsson, M, Leander, J, Fahlman, J, Brodin, T, Fick, J, & Hellstrom, G (2019) Less anxious salmon smolt become easy prey during downstream migration. Sci Total Environ 687(15):488-493.
Nikolaou, A, Meric, S & Fatta, D (2007) Occurrence patterns of pharmaceuticals in water and wastewater environments. Anal Bioanal Chem 387: 1225–1234 (2007). doi:10.1007/s00216-006-1035-8
Oceana (n.d.) Atlantic Salmon. Retrieved March 6, 2022.
Singh R & Abdijadid S (n.d.) Oxazepam. StatPearls [Internet].
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