If you figured it out the hint from the previous post, we are talking about bats today!! As we all know, bats are nocturnal animals which basically means they are active during the night and probably sleeping in the day.

So how does light pollution affect bats?

First let us look at how street lighting affects commuting bats. Based on an experiment conducted, it was concluded that there was an negative effect on commuting behaviour of bats where bat activity was severely reduced and the “onset of commuting behaviour was delayed in the presence of lighting, with no evidence of habituation” (Stone et al., 2009). This means that artificial lighting then leads to bats altering the routes they take to travel between places. This experiment focused on a particular bat species called Rhinolophus hipposideros which is an endangered species. Since its already a slow flying species, perhaps it is now more vulnerable to predatory birds due to the disruptions in flight routes. This is because they respond to light disturbances in four ways: “flying above or around the lights, on the unlit side of the hedge, choose an alterative routes or return back to the roost” (Stone et al., 2009). When different routes than the original are taken, they are often more exposed to predators. Additionally, it is plausible that longer flight distances to foraging areas can affect bats’ fitness and thus reproduction (Stone et al., 2009).

Another research focused on investigating the energy metabolism in an insectivorous bats through plasma metabolite analysis by measuring ß-hydroxybutyrate in bats from both lit and unlit environments. The key finding was that “red bats actively forage around lights to take advantage of concentrated prey resources likely gaining some benefit, while big brown and gray bats avoid lit area” (Cravens & Boyles, 2019). This shows how the effects of ALAN is not the same for all species of bats. There seems to be different biological effects, as indicated by the different ß-hydroxybutyrate levels in bats (see diagram below), which then leads to different behaviours.

If you are still wondering why ß-hydroxybutyrate levels are measured, let me explain it to you in simpler terms. Basically, it is used as an indicator for foraging efficiency and thus energy gains by bats (Cravens & Boyles, 2019). However, defining ß-hydroxybutyrate levels as an indicator might not be entirely accurate. This because ß-hydroxybutyrate levels are also influenced by other factors like fasting. Thus, perhaps it might be a better indicator of energy than foraging efficiency. Also, artificial lighting might benefit red bats over other bats as insects concentrate in lit areas rather than the dark unlit areas (Cravens & Boyles, 2019). This would mean that other bats that avoid lit areas have a lower supply of insects to forage on. Thus, while some insectivorous bats can potentially benefit from artificial lighting, others do not.

If were to look at fruit-eating bats, there seems to be a negative impact on their behaviour. Specifically, it deters them from foraging from areas with fruiting plants which then leads to disruption of other ecosystem services where fruits are less likely to be harvested and dispersal of seeds is less likely (Lewanzik & Voigt, 2014). As concluded in the this research, the effects of artificial lighting is not limited to bats only but extend to the ecosystem services that they provide. Without seed dispersal by bats, might be detrimental to the maintenance of biodiversity in forest areas or agricultural areas.

Overall, we can see how bats can be both negatively and positively affected by artificial lighting as a result of light pollution. Artificial lighting alters bat behaviours as they naturally structure their behaviour on light and darkness which is also influenced by their bio-chemical responses.

Hope you learned a thing or two about bats 🙂

 

References

Cravens, Z.M. & Boyles, J.G. (2019) Illuminating the physiological implications of artificial light on an insectivorous bat community, Oecologia, vol. 189, no. 1, pp. 69-77.

Stone, E.L., Jones, G. & Harris, S. (2009) Street Lighting Disturbs Commuting Bats, Current biology, vol. 19, no. 13, pp. 1123-1127.

Science AAAS (2020) Available at: https://www.sciencemag.org/news/2020/08/australia-s-biggest-bats-fly-thousands-kilometers-year-farther-wildebeest-and-caribou [image]

---

Check out the next post 🙂